CIVITY NGE Blog

The BNG Spatial Risk Multiplier reduces the value of off-site biodiversity units when habitat compensation is located further from the biodiversity loss caused by a development. Under the current statutory biodiversity metric, area and hedgerow units within the same Local Planning Authority (LPA) or National Character Area (NCA) receive a multiplier of 1.0, neighbouring areas receive 0.75, and locations outside these areas receive 0.5. For developers using off-site biodiversity units to achieve biodiversity net gain, location can therefore directly affect how many units are required and, consequently, project costs. Understanding spatial risk early can help developers identify suitable units before finalising their BNG strategy and avoid sourcing units that lose a significant proportion of their value when entered into the statutory biodiversity metric. What Is the BNG Spatial Risk Multiplier? The BNG Spatial Risk Multiplier is a geographic scaling factor within the statutory biodiversity metric that reflects the relationship between biodiversity lost at a development site and habitat compensation delivered off-site. The principle is straightforward: off-site gains closer to the impact site retain more of their biodiversity unit value. More distant gains receive a reduced value within the metric. For area habitats and hedgerows, the current statutory metric applies the following spatial risk scores: Within: 1.0The off-site compensation is within the development site’s LPA boundary or National Character Area. Neighbouring: 0.75The compensation is outside the development site’s LPA or NCA but within a neighbouring LPA or NCA. Outside: 0.5The compensation is outside both the relevant and neighbouring LPA or NCA. This means an off-site habitat does not necessarily have to be within the same local planning authority to receive the full 1.0 multiplier. Being within the same National Character Area can also satisfy the current “within” category for area and hedgerow habitats. Why Does the Location of Off-Site BNG Units Matter? Location matters because the statutory biodiversity metric incentivises developers to deliver biodiversity gains close to where biodiversity is being affected. More distant off-site gains are discounted, which can increase the quantity of units needed to meet the development’s BNG requirement. This approach helps retain the ecological benefits of biodiversity enhancements closer to affected areas and local communities. For example, imagine that a habitat bank creates 10 biodiversity units before spatial risk is applied. If those units qualify for a 1.0 spatial risk multiplier, all 10 units retain their value for the development. At 0.75, the same 10 units contribute 7.5 units. At 0.5, they contribute only 5 units. The underlying habitat has not changed. What changes is the value attributed to those off-site gains for that particular development through the biodiversity metric. Government guidance confirms that biodiversity gains can be delivered anywhere in England, but the metric incentivises off-site gains closer to the development. It is therefore more accurate to say that developers are incentivised to source locally rather than saying off-site units must always come from the same LPA. How Do LPA and National Character Area Boundaries Affect Spatial Risk? For area habitats and hedgerows, the current metric considers both Local Planning Authority and National Character Area boundaries. An off-site site falling within either the same LPA or NCA as the impact site can receive the full 1.0 spatial risk score. This can considerably broaden the search area available to a developer. A habitat bank may sit outside the development site’s LPA but still share its National Character Area. In that situation, the units still qualify as “within” for spatial risk purposes. Conversely, a site outside both the relevant LPA and NCA may fall into the neighbouring or outside categories, reducing the effective biodiversity value of its units for that development. This is why searching for suitable off-site biodiversity units should consider both geographic frameworks rather than relying on the LPA boundary alone. Does the Spatial Risk Multiplier Work Differently for Watercourses? Yes. Watercourse habitats use catchment geography rather than LPA and National Character Area boundaries when determining spatial risk. Under the current statutory biodiversity metric, watercourse compensation within the same waterbody catchment receives a spatial risk score of 1.0. Compensation outside that waterbody catchment but within the operational catchment receives 0.75, while compensation outside the operational catchment receives 0.5. Different rules also apply to intertidal habitats, where Marine Plan Areas are used. Developers should therefore establish which habitat unit type they need before searching the private market for off-site BNG units. How Can Spatial Risk Increase the Number of BNG Units Required? A spatial risk deduction can mean a developer needs to purchase a greater quantity of off-site units because each unit contributes less towards the development’s BNG requirement. For example, suppose a development needs 6 effective off-site area habitat units. If suitable units qualify for the 1.0 multiplier, 6 units provide the required value. If otherwise suitable units receive a 0.75 multiplier, approximately 8 raw units would be needed to provide 6 effective units, subject to the wider metric calculation and trading rules. If the units receive a 0.5 multiplier, approximately 12 raw units would be required to provide the same 6 effective units. This simplified example demonstrates why the cheapest advertised unit price is not necessarily the cheapest solution for a development. Unit location and effective value need to be considered alongside price. How Does Spatial Risk Affect Project Costs? The Spatial Risk Multiplier can increase BNG costs because a lower multiplier may require the developer to secure more units to address the same biodiversity deficit. Developers comparing off-site options should therefore consider the effective cost of satisfying their requirement rather than comparing biodiversity units purely on their headline price. A lower-priced habitat bank further from the development could ultimately require more units. A more local habitat bank with a 1.0 multiplier could require fewer units and potentially provide a more efficient solution. Other factors remain important too. Habitat type, trading rules, availability, and the specific unit deficit identified in the developer’s biodiversity metric all influence which off-site solution is appropriate. This makes early assessment particularly valuable for financial planning. What Is the Difference Between Spatial Risk and Strategic Significance? Spatial risk and strategic significance are separate components of the biodiversity metric. Spatial risk considers the geographic relationship between the development’s biodiversity loss and off-site compensation, while strategic significance considers whether habitat creation or enhancement is located in an area identified as strategically important for nature recovery. Local Nature Recovery Strategies identify priorities and potential measures for recovering or enhancing biodiversity within their strategy areas. A habitat bank can therefore have advantages because of its strategic location, while spatial risk is considered separately within the metric. Developers should not assume that a strategically significant habitat automatically avoids a spatial risk deduction. Both factors need to be correctly entered and assessed within the statutory biodiversity metric. Do BNG Trading Rules Still Apply to Local Off-Site Units? Yes. A favourable BNG Spatial Risk Multiplier does not override the statutory metric’s trading rules. Trading rules help prevent losses of more valuable habitats from being compensated through inappropriate lower-distinctiveness habitats. Developers therefore need to source the right habitat types and biodiversity units, not simply the closest available units. A habitat bank within the same LPA or National Character Area may receive a spatial risk score of 1.0 but still be unsuitable if its available units do not satisfy the development’s habitat requirements and trading rules. The correct approach is therefore to consider habitat type, distinctiveness, unit availability, trading rules and spatial risk together. When Should Developers Start Looking for Off-Site BNG Units? Developers should investigate off-site options once their biodiversity metric is sufficiently developed to indicate the likely type and quantity of off-site units required. Waiting until the final stages of the planning process can reduce the range of available units, particularly where specific habitat types are in demand. Early market assessment allows developers to compare habitat banks across the relevant LPA and National Character Area, understand how the Spatial Risk Multiplier affects each option and obtain realistic cost information. The metric may change as the development layout evolves. Updated calculations can therefore be used to obtain revised quotations and understand how design decisions affect the off-site requirement. Where the right unit type is in short supply or favourable pricing is available, developers may also wish to explore whether units can be reserved or secured with a deposit. How Does Spatial Risk Relate to the Biodiversity Gain Plan? Where off-site units form part of a development’s BNG strategy, the final biodiversity metric calculation and off-site allocation feed into the Biodiversity Gain Plan. Off-site gains must be registered on the Biodiversity Gain Sites Register and allocated to the relevant development before they can count towards its BNG requirement. The local planning authority can then check that the off-site gains included within the Biodiversity Gain Plan correspond with the relevant registered allocation. This makes selecting suitable off-site provision more than a procurement decision. The units need to work within the statutory biodiversity metric, satisfy applicable trading rules and be correctly registered and allocated. How Do Statutory Biodiversity Credits Compare? Statutory biodiversity credits are a last-resort option where a developer cannot achieve the required biodiversity net gain through on-site or off-site delivery. A spatial risk adjustment also applies to statutory biodiversity credits. Each statutory credit provides 0.5 biodiversity units, meaning developers need to purchase two statutory credits for every one biodiversity unit required. Credits are priced in tiers according to habitat type, with different prices applying depending on the habitat being compensated. This can make statutory credits a significantly more expensive option than securing suitable off-site biodiversity units, reinforcing the importance of exploring appropriate private-market off-site solutions first. How Civity Helps Developers Find Suitable Off-Site BNG Units At Civity, we help developers interpret the completed biodiversity metric outputs supplied by their ecological team and identify the off-site biodiversity units required to satisfy their remaining BNG obligation. We do not undertake the developer’s biodiversity metric calculation. Instead, we use the completed metric to understand the required habitat types and unit quantities before identifying suitable off-site options. Location forms an important part of that process. We can consider the development site’s LPA and National Character Area alongside our available habitat bank units to understand how spatial risk may affect the value of different options. We can then provide fast quotations for suitable off-site BNG units, helping developers compare the commercial implications of their available options. Because development layouts and biodiversity metric calculations often evolve, Civity can also provide revised quotations as the unit requirement changes. This gives project teams greater visibility over potential BNG costs throughout the planning process. Our work with habitat banks and landowners also gives us visibility across the supply side of the BNG market, helping connect appropriate habitat creation and enhancement opportunities with genuine developer demand. Why Early Site Selection Matters for Off-Site BNG The location of off-site biodiversity units can materially change their effective value within the statutory metric, making site selection an important part of a developer’s BNG strategy. Under the current rules, area and hedgerow units within the same LPA or National Character Area can retain their full value through a 1.0 spatial risk multiplier. Neighbouring locations receive 0.75, while more distant provision receives 0.5. However, proximity is only part of the decision. Suitable units must also meet the project’s habitat requirements and statutory trading rules. By assessing spatial risk, habitat type, availability and price together, developers can make more informed decisions about their off-site BNG strategy and understand the likely cost before their Biodiversity Gain Plan is finalised. For support identifying and pricing suitable off-site units, speak to Civity about your development’s BNG requirements.

Since mandatory biodiversity net gain (BNG) became a legal requirement in England on 12 February 2024, biodiversity has become a central consideration within the planning process. Before development can begin, local planning authorities must approve a biodiversity gain plan demonstrating how a development will achieve at least a 10% increase in biodiversity value. Many developers assume that submitting biodiversity metric calculations alone is enough. In practice, local planning authorities look for much more than a final biodiversity score. They want evidence that biodiversity net gain requirements have been properly considered throughout the design process, that biodiversity gains are realistic and deliverable, and that they will be maintained for at least 30 years. Understanding what local planning authorities actually look for can help reduce planning risk, avoid delays and improve the likelihood of securing planning permission. The Purpose of a Biodiversity Gain Plan A biodiversity gain plan is the document that shows how a development will achieve biodiversity net gain and satisfy the biodiversity gain condition attached to planning permissions. It accompanies the finalised statutory biodiversity metric tool and comprises a simple pro-forma, onto which a number of other documents and agreements may be appended depending on the complexity of the project. Under the statutory framework, local planning authorities must approve the biodiversity gain plan before development starts. LPAs generally have up to eight weeks to determine whether the submitted gain plan satisfies biodiversity net gain requirements. The gain plan forms part of the wider biodiversity net gain BNG process and demonstrates how biodiversity value will be protected, enhanced and maintained throughout the lifecycle of a development project. Accurate Baseline Biodiversity Value Calculations One of the first things planning authorities assess is whether the baseline biodiversity value has been calculated correctly. The pre-development biodiversity value establishes the benchmark against which biodiversity gain is measured. Local planning authorities will expect developers to provide accurate habitat surveys undertaken by suitably qualified professionals and supported by ecological expertise. The statutory biodiversity metric tool must be used to calculate the baseline biodiversity value. Published by Natural England, the current biodiversity metric calculates biodiversity units based on habitat size, condition and distinctiveness. Local planning authorities will review whether the baseline biodiversity has been assessed accurately within the red line boundary and whether existing habitat conditions have been properly recorded. Evidence That the Biodiversity Gain Hierarchy Has Been Followed Many local planning authorities place significant emphasis on the biodiversity gain hierarchy and mitigation hierarchy. Before considering off-site biodiversity units, developers must demonstrate that opportunities to avoid biodiversity loss have been fully explored. Planning officers want to see evidence that site layouts have been designed to retain valuable habitats, protect biodiversity and minimise impacts on wildlife habitats and wildlife species. Particular attention is often given to irreplaceable habitats. LPAs will check that adverse impacts on irreplaceable habitats have been minimised and that statutory requirements relating to these habitats have been followed. Where biodiversity losses cannot be avoided, authorities expect developers to maximise habitat enhancement and habitat creation opportunities within the development site before relying on off-site gains. Robust Biodiversity Metric Calculations A biodiversity gain plan must contain clear and transparent biodiversity metric calculations. Planning authorities will review both the pre-development biodiversity value and the projected post-development biodiversity value to ensure that the biodiversity gain objective is being met. The statutory biodiversity metric measures biodiversity value before and after development and calculates whether sufficient biodiversity units have been delivered to achieve mandatory biodiversity net gain. Authorities will scrutinise habitat creation assumptions, habitat enhancement works, habitat condition targets and delivery timescales. Unrealistic assumptions can result in requests for additional information or delays to approval. Clear On-Site Biodiversity Proposals Local planning authorities generally prefer biodiversity gains to be achieved on site wherever possible. A strong biodiversity gain plan should clearly explain how biodiversity gains will be delivered through habitat creation, habitat enhancement and green infrastructure. This may include new woodland planting, species-rich grassland creation, wetland features, wildlife corridors or other measures designed to enhance biodiversity. Planning officers will assess whether proposed habitats are appropriate for the location and whether they contribute positively to the natural environment and local nature recovery objectives. Developers should clearly explain how much biodiversity gain can be achieved on site and how these measures contribute to the overall net gain target. Should proposed on-site habitats that contribute to the overall net gain score require specific management regimes, it may be necessary to append a detailed habitat management plan and a 30+ year legal commitment to enact that plan (such as a Section 106 agreement). Appropriate Off-Site Biodiversity Gains Where sufficient biodiversity units cannot be achieved on site, LPAs will assess proposed offsite biodiversity units carefully. If biodiversity gain requirements cannot be achieved on-site, off-site biodiversity gains must be legally secured and registered. Local planning authorities will expect evidence that the proposed biodiversity gain site appears on the Biodiversity Gain Site Register maintained by Natural England. Authorities will also review whether off-site gain sites align with local nature recovery strategies and broader local nature recovery priorities. Sites that contribute to strategic ecological objectives often carry greater strategic significance within the statutory biodiversity metric. Many local planning authorities favour off-site biodiversity units located within their own authority area where possible, particularly where these support local habitat creation priorities. Legal Agreements and Long-Term Security One of the most important aspects of any biodiversity gain plan is demonstrating that biodiversity gains will be maintained over the long term. Biodiversity net gain must be secured for a minimum of 30 years. Local authorities therefore require evidence that appropriate legal agreements are in place. For offsite biodiversity units, this may involve conservation covenants with a responsible body or planning obligations secured through Section 106 agreements. These legal mechanisms ensure biodiversity gain commitments remain enforceable long after planning permission has been granted. Planning authorities will often review the legal agreement alongside the biodiversity gain plan to ensure habitats are properly protected. Habitat Management and Monitoring Plans (HMMPs) Delivering biodiversity gain is only part of the requirement. Authorities also want to understand how habitats will be managed. A detailed monitoring plan should explain how biodiversity gains will be maintained and monitored over the required 30-year period. The management plan should identify responsibilities, maintenance activities, performance indicators and reporting arrangements. If purchasing biodiversity units from an offset provider such as Civity, they will have their own pre-approved HMMP; however, if providing your own habitats, you may be expected to produce your own project-specific HMMP and to secure it via an appropriate legal agreement over the 30-year period.  Local planning authorities have a duty to monitor biodiversity gains and verify compliance throughout the management period. As a result, clear environmental management arrangements are increasingly important within planning submissions. Off-Site Units and Statutory Biodiversity Credits Where offsite biodiversity units are required, planning authorities will expect developers to provide evidence that those units have been secured appropriately. This includes demonstrating that the biodiversity value of the proposed gains equals or exceeds the value being claimed within the biodiversity metric calculations. Where developers intend to buy statutory biodiversity credits, LPAs will typically require evidence that statutory credits have been purchased. However, statutory biodiversity credits are intended as a last resort and should only be used where suitable off-site biodiversity gains cannot be secured through the private market. It will be necessary to demonstrate to the LPA that it was not practicable to produce units or purchase them from an offset provider before resorting to purchasing statutory credits. The biodiversity Gain Plan template stipulates that at least three offset providers or a negative search result from online registers is required as evidence, but this should be treated as a minimum requirement and LPAs may have more detailed thresholds. Alignment with Local Nature Recovery Strategies Local nature recovery strategies are becoming increasingly influential within planning decision-making. Many local planning authorities assess whether biodiversity gains contribute towards local nature recovery priorities. Habitat creation proposals that support strategic ecological networks, wildlife habitats and biodiversity enhancement objectives are often viewed more favourably. Developers who align biodiversity gain plans with local nature recovery strategies can often strengthen their planning submissions while delivering wider environmental benefits. How Civity Supports Biodiversity Gain Plan Preparation At Civity, we support developers throughout the biodiversity net gain process, from baseline biodiversity assessments and statutory biodiversity metric calculations through to biodiversity gain plan preparation and off-site biodiversity unit procurement. Our team works closely with developers, ecologists, land managers and local planning authorities to ensure biodiversity gain plans are robust, compliant and aligned with planning policy requirements. We also help clients identify suitable habitat banks, secure offsite biodiversity units and navigate the legal requirements associated with conservation covenants and planning obligations. Conclusion What local planning authorities actually look for in a biodiversity gain plan goes far beyond achieving a numerical biodiversity target. Planning authorities want evidence that baseline biodiversity has been assessed correctly, that the biodiversity gain hierarchy has been followed, that biodiversity units are calculated accurately and that habitats will be managed successfully for at least 30 years. Developers who address these requirements early and prepare a comprehensive biodiversity gain plan are far more likely to achieve planning permission efficiently while delivering meaningful biodiversity gains for the natural environment.

Mandatory biodiversity net gain (BNG) has been in place since the Environment Act 2021 and is now a key aspect of the planning system. Developers are now required to demonstrate at least a 10% increase in the value of biodiversity and to meet the statutory biodiversity gain criteria before they can start on development sites. The notion of biodiversity net gain is basic, but a lot of planning delays are now occurring because BNG requirements are being addressed too late in the project lifetime. Problems such as incomplete biodiversity gain plans, incorrect biodiversity metric calculations and no offsite biodiversity increases might delay planning authorisation. Identifying early on where the risks lie and how to mitigate them can help ensure a smoother planning process and save costly redesigns or delays. 1. Perform Biodiversity Surveys Before Site Design One of the most typical planning concerns is the delay of biodiversity evaluations until site layouts have been developed. At the earliest stage, a suitably qualified ecologist should be commissioned to survey the development site and quantify the pre-development biodiversity value using the statutory biodiversity metric. The statutory biodiversity metric assesses biodiversity value using habitat data. It establishes the baseline biodiversity against which all future biodiversity improvements will be assessed. The pre-development biodiversity value forms the foundation of every biodiversity gain plan and is used to calculate both the baseline biodiversity and the required post-development biodiversity value needed to achieve the biodiversity gain objective. Early ecological surveys help to identify existing habitats, priority species, irreplaceable habitats and other ecological restrictions before site design is finalised. This enables biodiversity issues to be integrated into development projects from the start of the process rather than at a late point as a barrier. 2. Design for the Biodiversity Gain Hierarchy One of the most fundamental aspects of biodiversity net gain is the biodiversity gain hierarchy. Developers should follow a precise sequence of actions: eliminate impacts where possible, minimise unavoidable impacts, restore habitats where appropriate, deliver significant onsite habitat enhancements and only then consider off-site gains. This approach helps maintain the integrity of the natural environment while reducing reliance on biodiversity credits and statutory biodiversity credits. The mitigation hierarchy remains fundamental to planning, decision-making and biodiversity net gain standards. Often, retaining mature trees, ponds, hedgerows and other elements of high-value habitat reduces biodiversity loss and reduces the number of units of biodiversity that need to be replaced elsewhere. It is generally cheaper to design for existing biological value than to rely on substantial biodiversity credits or off-site solutions. 3. Early Consultation with Local Planning Authorities Local planning authorities have a key role in assessing biodiversity gain plans and monitoring compliance with biodiversity gain conditions. Engaging with local authorities early on in the project development can allow developers to grasp local planning expectations, local nature recovery strategy priorities and any site-specific biodiversity implications. Many local planning authorities have created local enforcement plans and monitoring arrangements in support of the implementation of mandated biodiversity net gain. Early engagement might help minimise surprises later on in the planning phase and match biodiversity initiatives with local interests. 4. Develop a Strong Biodiversity Gain Strategy For most developments a biodiversity gain plan is now a basic planning requirement. The plan must demonstrate the pre-development biodiversity value, the expected post-development biodiversity value and how the biodiversity gain objective will be attained through onsite biodiversity gains, habitat creation and ongoing management. It should also clearly set out ideas for habitat construction, habitat augmentation strategies, ongoing management procedures and monitoring criteria. Although not always required, it may make sense (particularly for larger or more complex projects) to submit a Biodiversity Gain Plan as part of the planning application itself; this gives the Planning Authority a chance to comment on the proposed BNG strategy prior to granting consent. A robust pre-consent biodiversity gain plan should also include a draft habitat management strategy, maintenance mechanisms and a monitoring plan covering both the initial delivery and long-term habitat management. Where phased developments are proposed, an overall biodiversity gain plan should be created before construction starts. The statutory biodiversity gain condition is a pre-commencement condition linked to planning licenses. The biodiversity gain plan has to be authorised before development commences. Incomplete or poorly prepared submissions continue to be one of the most prominent reasons for planning delays. 5. Attain Early Offsite Biodiversity Gains Many developments cannot meet the full 10% biodiversity net gain threshold through on-site habitat upgrades alone. Where substantial on-site habitat enhancements are not possible, developers will have to achieve off-site biodiversity advantages. Ideally these off-site gains should be secured as early as feasible, prior to planning application submissions. Off-site biodiversity units are available to varying degrees based on habitat type, location and market need. Units within the same local planning authority area frequently have a higher biodiversity value within the measure and may be preferred by planning authorities. All offsite biodiversity gains that are registered must be legally secured and recorded on the Biodiversity Gain Site Register maintained by Natural England. Sourcing units to have them on site while waiting for planning permission might generate extra risk, especially with major building initiatives. 6. Establish Long-Term Management Arrangements BNG compliance doesn’t stop after planning clearance is obtained. Initial delivery and continuous management of habitats must be assured for at least 30 years. Developers need to establish a draft habitat management strategy early and define who will be accountable for habitat care, monitoring and reporting. Whether given on site or through offsite biodiversity benefits, the procedures for maintenance should be explicitly recorded through planning obligations, conservation covenants or other legally secured agreements. A detailed monitoring plan assists local authorities to achieve effective monitoring and to properly track gains in biodiversity during the life of the project. 7. Know Your Last Resort Options If onsite habitat enhancements or registered offsite biodiversity gains cannot meet biodiversity gain targets, statutory biodiversity credits may be obtained. However, developers can only buy statutory biodiversity credits after demonstrating that all reasonable alternatives have been considered. These statutory credits are purposefully expensive and are meant as a last resort, not a first choice. Wherever possible developers should look for off-site solutions rather than rely on biodiversity credits bought through the government plan. Common BNG Risks Delaying Planning Permission There are still a number of recurring difficulties that cause delays across the planning system. These include incorrect estimations of biodiversity metrics, incomplete biodiversity gain plans, poor habitat management suggestions and failure to demonstrate conformity with the biodiversity gain hierarchy. Other issues include undervaluing the onsite environment, not securing offsite biodiversity gains early enough and ignoring local planning authority regulations. With biodiversity gain criteria attached to most planning licenses given after 12 February 2024, these challenges are becoming increasingly vital for developers to resolve proactively. How Civity Helps with BNG Planning Risk At Civity, we support developers in delivering biodiversity net gain requirements from initial feasibility through to planning approval and delivery. We offer support with biodiversity assessments, statutory biodiversity metric calculation, biodiversity gain programmes, habitat creation strategies and offsite biodiversity unit purchase. We also advise clients on finding appropriate habitat banks, obtaining legally compliant off-site gains, and preparing feasible long-term monitoring programmes. Early consideration of biodiversity needs can help developers mitigate planning risk, increase project certainty and avoid costly last-minute delays.

One of the most common questions developers ask is, ‘When should you start sourcing off-site BNG units?’ The simple answer is as early as possible. Under the mandatory biodiversity net gain (BNG) framework introduced by the Environment Act, developers must achieve at least a 10% biodiversity net gain before development can commence. While many schemes can deliver some biodiversity gain on-site, a significant number of development projects require off-site biodiversity units to bridge the gap between the pre-development biodiversity value and the required post-development biodiversity value. Leaving off-site BNG procurement until the end of the planning process can create delays, increase costs and limit the availability of suitable units. Understanding the correct timeline can help secure planning permission efficiently and meet biodiversity obligations. Understanding Mandatory Biodiversity Net Gain Mandatory biodiversity net gain began in England in early 2024. Major developments became subject to mandatory BNG from 12 February 2024, while small sites followed on 2 April 2024. Nationally Significant Infrastructure Projects will be subject to BNG requirements from November 2026. Under the legislation, developers must demonstrate a minimum 10% net gain in biodiversity value using the statutory biodiversity metric. This information is submitted through a biodiversity gain plan, which must be approved before development starts. The biodiversity gain plan forms a key part of the wider planning process and demonstrates how biodiversity gains will be delivered through onsite habitat enhancement, habitat creation and, where necessary, offsite biodiversity gains. Stage 1: Feasibility and Baseline Assessment The earliest opportunity to consider off-site biodiversity units is during the feasibility stage. Before finalising any design work, developers should carry out biodiversity assessments to establish the baseline biodiversity of the development site. This includes identifying habitats, assessing existing ecological value and calculating baseline biodiversity units using the statutory biodiversity metric tool. The assessment establishes the pre-development biodiversity value and acts as an early indicator to identify whether the proposed scheme is likely to achieve biodiversity net gain through on-site delivery alone. At this stage, developers should already begin considering potential off-site solutions, particularly where significant biodiversity loss is anticipated. Stage 2: Concept Design and Biodiversity Metric Calculations As site design evolves, biodiversity metric calculations become increasingly accurate. The statutory biodiversity metric and associated on-site habitat survey assesses existing habitats, area habitat units, linear habitats and habitat condition to determine biodiversity value. It also calculates the projected post-development biodiversity value based on the building(s) footprint, proposed habitat enhancement works, and habitat creation measures. Where calculations indicate a shortfall, developers can begin estimating how many biodiversity units may be required from off-site habitats. This is the point at which many developers first engage with habitat bank operators and registered habitat banks to understand availability and indicative pricing. Stage 3: Applying the Biodiversity Gain Hierarchy Before sourcing off-site units, the biodiversity gain hierarchy must be followed. The hierarchy requires developers to prioritise habitat retention, onsite habitat enhancement and biodiversity improvements before relying on offsite biodiversity units. The mitigation hierarchy remains a fundamental principle of biodiversity net gain implementation. This means site design should focus on protecting existing habitats, enhancing biodiversity within the red line boundary and maximising site biodiversity units wherever possible. Only once these opportunities have been explored should developers move towards securing off-site gains. Stage 4: Pre-Application Planning The best time to actively pursue off-site biodiversity units is before submitting planning applications. At this stage, biodiversity metric calculations should be sufficiently developed to identify likely unit requirements. Developers can then engage with providers to check availability, obtain accurate pricing and, where appropriate, secure or reserve suitable units within the relevant local planning authority area. If the required habitat type is in limited supply or competitively priced, placing a deposit or reserving units early can help reduce the risk of delays and future price increases as the project progresses. Early engagement is important because off-site unit availability varies significantly by location, habitat type and demand. Prices also fluctuate depending on habitat distinctiveness, strategic significance and proximity to the development site. Units located within the same local planning authority area and aligned with local nature recovery strategy priorities generally achieve the highest ecological value within the metric. Starting early helps avoid situations where suitable units are unavailable when planning permission is approaching determination. Stage 5: Planning Submission At the planning submission stage, developers should have a near-final biodiversity metric calculation and sufficient ecological information to demonstrate how the scheme intends to achieve biodiversity net gain. While a formal Biodiversity Gain Plan is not submitted as part of the planning application, many developers choose to prepare a draft version to support discussions with the local planning authority and demonstrate that the proposed approach is achievable. Where significant on-site biodiversity gains, habitat creation or habitat enhancement are proposed, it is also good practice to prepare a draft Habitat Management and Monitoring Plan (HMMP). This helps show how new or enhanced habitats will be established, managed and maintained over the required 30-year period. Providing this information at the planning stage gives local planning authorities greater confidence that biodiversity net gain requirements can be delivered and may help resolve ecological queries earlier in the planning process. The formal Biodiversity Gain Plan is then submitted after planning permission has been granted and must be approved before development can commence. Stage 6: Securing Off-Site Units Before Development Starts Although planning permission may be granted before final allocation, developers must secure and allocate off-site biodiversity units before development commences. All off-site units must come from a registered biodiversity gain site listed on the Biodiversity Gain Site Register maintained by Natural England. The units must also be legally secured through a conservation covenant or planning obligation and supported by a long-term habitat management and monitoring plan. These legal agreements guarantee that biodiversity gains are maintained for at least 30 years. Once biodiversity credits are purchased and allocated, responsibility for delivering the biodiversity gains typically transfers to the habitat provider through the relevant legal framework. What If Suitable Off-Site Units Cannot Be Found? In some locations, particularly where demand is high, sourcing suitable off-site BNG units can be challenging. Where developers cannot secure sufficient units through the private market, statutory biodiversity credits may be available. However, developers can only purchase statutory biodiversity credits as a last resort after demonstrating that all other reasonable options have been explored. These statutory credits are intentionally priced at a premium to encourage investment in habitat creation and biodiversity gain sites rather than government-backed credits. Why Early Engagement Matters The most successful projects treat biodiversity net gain as a core part of site strategy from the outset. Early engagement allows developers to understand likely biodiversity obligations, estimate costs, secure unit availability and avoid delays during determination. It also improves site design by identifying opportunities for habitat retention and biodiversity enhancement before layouts become fixed. Waiting until planning permission is granted often reduces flexibility and can create unnecessary pressure on programme timelines. Expert Support for Off-Site BNG Units At Civity, we help developers navigate every stage of the BNG framework, from biodiversity assessments and metric calculations through to sourcing and securing off-site biodiversity units. Our team works with registered habitat banks and biodiversity gain sites across England, helping clients identify suitable units early in the planning process and secure compliant off-site BNG solutions aligned with local planning authority requirements. For developers looking to source units, our available inventory can be viewed through our BNG units for sale service, where we provide rapid pricing, availability checks and expert guidance tailored to individual development projects.

Since mandatory biodiversity net gain (BNG) became a legal requirement for most developments in England, developers have had to take a far more strategic approach to ecology during the planning process. Biodiversity is no longer something that can be considered once site plans have been finalised. Instead, it must be embedded into development proposals from the outset to achieve planning success and comply with current legislation. Introduced through the Environment Act 2021, biodiversity net gain requires most qualifying developments to deliver at least a 10% uplift in biodiversity value compared with the site’s existing biodiversity. This uplift must be demonstrated using the statutory biodiversity metric, supported by a Biodiversity Gain Plan, and maintained for a minimum of 30 years. For developers unable to achieve sufficient gains on-site, understanding the trading rules surrounding off-site biodiversity gains, off-site biodiversity units and statutory biodiversity credits has become increasingly important. However, biodiversity trading is tightly regulated and follows a clear hierarchy designed to protect the natural environment while improving biodiversity across England. In this guide, we explain how biodiversity net gain trading works, when biodiversity units can be purchased, and how expert ecological advice can help your project progress through the planning system with confidence. Understanding Biodiversity Net Gain Biodiversity net gain is an approach to development that ensures projects leave biodiversity in a measurably better state than before work begins. Since February 2024, mandatory biodiversity net gain has applied to planning permissions granted for most major developments, with qualifying small sites also becoming subject to the legislation shortly afterwards. While some developments remain exempt, including many householder applications, developments submitted before 12 February 2024, certain self-build projects and specific infrastructure schemes such as the high-speed rail network, the majority of development proposals must now comply with biodiversity net gain requirements. To demonstrate compliance, developers must calculate both the pre-development biodiversity value and the anticipated post-development biodiversity value using the statutory biodiversity metric. The Biodiversity Metric assesses habitat size, habitat type, habitat condition and the strategic significance of habitats to generate biodiversity units that can be compared before and after development. Planning authorities expect every qualifying scheme to demonstrate at least a 10% biodiversity uplift before development begins, making biodiversity net gain BNG an essential part of modern planning. Why Biodiversity Trading Rules Exist Many people assume biodiversity trading simply involves purchasing biodiversity units whenever ecological losses occur. In reality, the system is designed to ensure that biodiversity improvements happen in the right places and only after every reasonable opportunity has been taken to retain and enhance biodiversity on the development site itself. Trading rules stipulate a directional manner in which habitats can be traded based on their rarity and inherent ecological value; in simplified terms, it ensures that common habitat types can be replaced with rare habitat types, but not the other way around. The most common habitats may be offset by creation of any other habitat; less common habitats must be replaced on a roughly like-for-like basis or better; rare habitats still (those with high distinctiveness) must be replaced on a like-for-like basis; and the most valuable habitats must be replaced on a like-for-like basis and with bespoke compensation and consideration required for any loss. The biodiversity trading rules are intended to deliver genuine environmental improvements rather than allowing biodiversity losses to be offset too easily. Habitat improvements must represent measurable gains beyond what would have happened naturally, while biodiversity trading should contribute towards wider ecological networks and support local nature recovery strategies. For this reason, planning authorities carefully assess how developers have applied the Biodiversity Gain Hierarchy before considering proposals that rely on off-site solutions. The Biodiversity Gain Hierarchy Comes First The biodiversity gain hierarchy sits at the centre of biodiversity net gain policy and underpins every biodiversity gain plan submitted as part of the planning process. Before developers can consider purchasing biodiversity units, they must demonstrate that they have followed the hierarchy correctly. The first priority is to avoid biodiversity loss wherever possible by protecting existing habitats, preserving ecological features and designing development around areas of ecological importance. Early master planning gives developers the best opportunity to retain valuable habitats while reducing environmental impacts. Where habitat loss cannot be avoided, the next step is to minimise impacts through sensitive site design before delivering on-site gains using habitat enhancement and habitat creation measures. Examples include creating species-rich grassland, native woodland planting, wetlands, green infrastructure, wildlife corridors and sustainable drainage systems that provide both environmental and community benefits. Only once these opportunities have been fully explored should developers consider off-site biodiversity gains. Planning authorities will often scrutinise proposed site plans to ensure the hierarchy has been followed correctly before approving any reliance on off-site units or biodiversity credits. Calculating Biodiversity Value Using the Statutory Biodiversity Metric Understanding biodiversity trading begins with understanding how biodiversity value is measured. The statutory biodiversity metric, published by Natural England, calculates changes in biodiversity by comparing the pre-development biodiversity value of a site with its expected post-development biodiversity value. The Biodiversity Metric generates biodiversity units by assessing several key characteristics, including habitat size, habitat type, habitat condition and strategic significance. Different habitat categories, such as woodland, grassland, wetlands or linear habitat, are assessed separately because habitat units cannot be traded between different habitat types. For example, biodiversity units lost from woodland cannot simply be replaced with grassland units elsewhere. Like-for-like or better compensation is generally required to ensure habitat losses are addressed appropriately and ecological function is maintained. The statutory biodiversity metric must be completed by professionals with appropriate ecological expertise, helping to ensure biodiversity metric calculations accurately reflect the ecological value of the site and comply with current guidance. Preparing a Biodiversity Gain Plan A compliant biodiversity gain plan is fundamental to achieving planning success. Although planning permission may already have been granted, developers cannot commence work until the Biodiversity Gain Plan has been submitted and approved by the relevant planning authority. The plan must demonstrate how the development will achieve at least a 10% biodiversity uplift while complying with biodiversity net gain requirements. The Biodiversity Gain Plan includes the site’s baseline biodiversity value, biodiversity metric calculations, details of habitat creation and habitat enhancement proposals, expected post-development biodiversity value and long-term management arrangements. Where off-site gains are required, the Biodiversity Gain Plan must also explain how these biodiversity units will be secured and managed. It should include a detailed habitat management and monitoring plan, setting out how biodiversity improvements will be maintained throughout the required 30-year period. Local planning authorities generally have up to eight weeks to determine whether the Biodiversity Gain Plan satisfies the biodiversity gain condition, although they may request additional information where further ecological evidence is required. Protecting Existing Habitats Before Considering Off-Site Solutions One of the most important principles within biodiversity net gain is that protecting valuable habitats should always take priority over replacing them elsewhere. The habitat trading rules (which categorise habitats by distinctiveness: low, medium, high and very high) give a good initial measurement for where to especially prioritise retention and safeguarding/enhancing over loss and replacement: the higher the distinctiveness, the more important it is likely to be to avoid impacts on that habitat parcel. Developers are encouraged to integrate ecology into master planning from the earliest stages of project design, identifying opportunities to retain mature vegetation, protect existing biodiversity and incorporate enhanced habitats into development layouts. Particular attention is given to priority habitats, ancient woodland and other areas of exceptional ecological importance. Some irreplaceable habitats are excluded from the standard 10% biodiversity net gain requirement because they cannot realistically be recreated elsewhere. Instead, developments affecting these habitats require careful consideration and may be subject to separate planning policies. Urban development sites often face greater challenges in delivering sufficient onsite habitat creation due to space constraints. However, planning authorities still expect developers to demonstrate that all reasonable onsite opportunities have been explored before proposing offsite options. By embedding biodiversity into site design from the outset, developers frequently reduce their reliance on biodiversity trading while creating developments that contribute positively to local ecosystems and the wider natural environment. Purchasing Off-Site Biodiversity Units Where a development cannot achieve the required biodiversity uplift through onsite habitat creation alone, developers may need to consider purchasing offsite biodiversity units. However, this option should only be explored after the Biodiversity Gain Hierarchy has been fully applied. Planning authorities expect developers to demonstrate that opportunities to protect existing biodiversity, retain valuable habitats, minimise habitat loss and deliver onsite habitat enhancement have been exhausted before relying on off-site biodiversity gains. Offsite biodiversity units are generated through habitat banks or dedicated biodiversity gain sites where landowners create, enhance and manage habitats specifically to provide measurable biodiversity gains. These biodiversity units can then be allocated to qualifying developments that are unable to achieve their required net gain on site. Choosing appropriate off-site units requires careful ecological assessment. The habitats being created should provide like-for-like or better ecological compensation wherever possible, taking account of habitat type, ecological importance, strategic significance and local planning priorities. Working with experienced ecological consultants ensures developers purchase the correct biodiversity units while avoiding unnecessary costs or delays during the planning process. Biodiversity Gain Site Register and Habitat Banks Before off-site biodiversity units can contribute towards a development’s Biodiversity Gain Plan, they must generally be secured from an approved biodiversity gain site. Eligible sites are entered onto the Biodiversity Gain Site Register, providing transparency over where off-site biodiversity gains are being delivered and ensuring they meet the legal requirements established under biodiversity net gain legislation. Many habitat banks create new habitats, restore degraded land or enhance existing habitats to generate biodiversity units that can be allocated to future developments. These projects not only help individual developments achieve compliance but also support wider ecological networks and local nature recovery strategies. Selecting the right biodiversity gain site is about more than simply purchasing enough biodiversity units. Developers should also consider habitat categories, ecological connectivity and whether the proposed habitat contributes positively to local biodiversity priorities. When Are Statutory Biodiversity Credits Used? If suitable offsite biodiversity units cannot be secured, developers may be able to purchase statutory biodiversity credits from the government. Statutory biodiversity credits are intentionally designed as a last resort rather than a routine solution. Developers must first demonstrate that they have fully explored opportunities to achieve biodiversity gains on site and investigated appropriate off-site solutions before statutory biodiversity credits will be considered. This approach reinforces the principle that biodiversity improvements should ideally be delivered as close as possible to the affected development site while supporting meaningful ecological recovery. A biodiversity net gain consultant can advise whether statutory biodiversity credits are appropriate for a particular scheme and help developers demonstrate compliance with the relevant trading rules where their use becomes necessary. Securing Biodiversity Gains Through Legal Agreements Purchasing biodiversity units alone is not enough to satisfy biodiversity net gain requirements. The long-term delivery of off-site gains must be legally secured to ensure habitats are created, managed and maintained for the required period. This is typically achieved through legal agreements, planning obligations or a conservation covenant. These legal mechanisms ensure that habitat creation and habitat enhancement are protected for a minimum of 30 years, providing certainty for developers, landowners, planning authorities and local communities. Without appropriate legal security, off-site biodiversity units cannot normally be relied upon when preparing a biodiversity gain plan. Experienced ecological advisers can work alongside legal teams to ensure biodiversity commitments are properly documented and meet current planning requirements. Long-Term Habitat Management and Ongoing Monitoring Biodiversity net gain does not end once planning permission has been granted or construction has finished. Developers must demonstrate that biodiversity improvements will continue to deliver measurable ecological benefits throughout the required management period. Every biodiversity gain plan should therefore include a detailed monitoring plan and habitat management and monitoring plan explaining how habitats will be maintained for at least 30 years. Long-term habitat management may include vegetation management, invasive species control, ecological surveys, water management, grazing regimes or woodland management depending on the habitat type being created. Regular ongoing monitoring allows habitat performance to be assessed over time and helps identify any issues that could affect compliance with planning conditions. If habitats are not developing as anticipated, corrective management measures can be implemented before biodiversity value is affected. Effective monitoring provides reassurance to planning authorities that biodiversity improvements remain genuine, measurable and capable of delivering lasting environmental benefits. Common Biodiversity Trading Mistakes Navigating biodiversity trading rules can be challenging, particularly for developers unfamiliar with mandatory biodiversity net gain. One of the most common mistakes is leaving biodiversity assessments until late in the planning process. This often limits opportunities to redesign development proposals, resulting in greater reliance on expensive off-site solutions. Another frequent issue is assuming biodiversity units are interchangeable. Because habitat units are assessed separately across different habitat categories, losses in one habitat type cannot simply be replaced with unrelated habitats elsewhere. Developers may also underestimate the importance of strategic significance, habitat quality or existing biodiversity when completing biodiversity metric calculations. These factors directly influence biodiversity value and therefore affect how many biodiversity units are required. Finally, failing to secure legal agreements or prepare a robust monitoring plan can delay planning approval even where sufficient biodiversity units have already been identified. Engaging ecological expertise at the earliest opportunity helps developers avoid these issues while improving planning outcomes. How Civity Can Help At Civity, we help developers, landowners and project teams confidently navigate the complexities of biodiversity net gain and biodiversity trading. Where on-site enhancements alone cannot deliver the required biodiversity uplift, we help clients identify appropriate off-site biodiversity units, assess suitable habitat banks and advise on statutory biodiversity credits where necessary. We also assist with habitat management and monitoring plans, conservation covenants and the legal arrangements required to secure biodiversity gains over the long term, helping clients progress projects efficiently while remaining fully compliant with biodiversity net gain requirements. Conclusion Understanding biodiversity trading rules is now an essential part of achieving planning success. Mandatory biodiversity net gain has introduced a structured framework that prioritises protecting existing biodiversity, enhancing habitats on site and using off-site solutions only where necessary. By following the biodiversity gain hierarchy, preparing a robust biodiversity gain plan and applying the statutory biodiversity metric correctly, developers can satisfy planning authorities while delivering meaningful environmental improvements. Working with experienced ecological consultants from the earliest stages of a project allows biodiversity to be integrated into development proposals rather than treated as a planning obstacle. This reduces planning risk, supports compliance with current legislation and helps create developments that contribute positively to both local ecosystems and wider nature recovery objectives. At Civity, we provide the ecological expertise and practical guidance needed to navigate biodiversity net gain trading rules with confidence, helping developers secure planning permission while delivering measurable, long-term benefits for the natural environment.