CIVITY NGE Blog

Biodiversity net gain is judged on delivery, not intention. Since mandatory biodiversity net gain became a legal requirement under the Environment Act 2021, developers must show that biodiversity value will increase by at least 10%, measured in biodiversity units using the statutory biodiversity metric. What often receives less attention is the other half of the system. Monitoring BNG is how local planning authorities, land managers and responsible bodies make sure those biodiversity gains are actually delivered on the ground and maintained for the full term. For clients working with Civity, monitoring is not a bolt-on after planning permission. It is embedded in the biodiversity gain plan, tied to legal agreement structures, and essential to proving that post-development biodiversity value matches what the biodiversity metric calculations predicted. Government guidance is explicit that gains must be secured and managed for a minimum of thirty years and that monitoring plans should show how this will happen in practice. Why monitoring sits at the core of biodiversity net gain BNG is built around a before-and-after comparison. The statutory metric uses baseline biodiversity within the red line boundary to calculate pre-development biodiversity value, then forecasts post-development values based on habitats created, habitats enhanced, and any habitat loss that cannot be avoided. Those forecast figures are meaningful only if the habitats that underpin them are delivered and sustained long-term. Monitoring BNG therefore protects the integrity of the gain hierarchy. It ensures that significant on-site gains and on-site habitat creation are not overstated, that off-site biodiversity units are genuinely implemented, and that statutory biodiversity credits remain a last resort rather than a default option. The Habitat Management and Monitoring Plan (HMMP) and what the Government expects The government sets out clear expectations in its guidance on a Habitat Management and Monitoring Plan (HMMP) for BNG. This plan is often the most operational part of a biodiversity gain plan. It explains how habitats created or improved will reach their target condition, how habitat changes will be tracked, and how progress will be assessed over the thirty-year requirement. A well-prepared HMMP should link directly to statutory biodiversity metric outputs. If a site is relying on highly distinct habitats, linear habitats such as hedgerows, or more complex habitat enhancement, the monitoring plan should reflect the longer time to target condition and higher delivery risk that the statutory biodiversity metric tool factors into biodiversity units. Government and Natural England have also produced templates to standardise management and monitoring submissions, helping local planning authorities review plans consistently. Establishing the baseline and setting realistic targets Effective monitoring starts with a reliable baseline. The baseline biodiversity value must be based on robust survey data for existing habitat within the development site, recorded correctly in the statutory biodiversity metric or small sites metric. If the baseline is inaccurate, the question of how many units are required becomes unclear, and monitoring later cannot prove that net gain has been achieved. Targets should then mirror what the biodiversity metric predicts. This means setting habitat condition goals that are realistic for the habitat type, the land management context, and the expected time needed for habitats created to mature. It also means describing what success looks like for strategic significance, particularly where local nature recovery strategies influence habitat priorities. Monitoring on-site gains through the development process On-site gains remain the first preference in mandatory BNG. Monitoring for on-site habitat creation/enhancement, therefore, needs to start early, tracking the implementation of habitat creation and habitat enhancement alongside construction. Local planning authorities will expect clear evidence that on-site habitats are delivered as planned and on schedule, that habitat lost during construction is not replaced by lower-value habitat categories, and that any invasive species risks are controlled so that biodiversity outcomes are not undermined. Where a scheme promises significant on-site gains, monitoring is crucial to ensuring those significant on-site gains are delivered; it also allows for adaptive management to respond to changing conditions throughout the thirty-year period. Government guidance makes it clear that significant on-site gains require the same thirty-year security and monitoring standards as off-site gains. Monitoring off-site biodiversity units and gain sites Many projects cannot achieve net gain entirely on-site. In these cases, monitoring extends to off-site solutions, whether delivered by a habitat bank, a landowner managing their own land, or another land manager providing off-site biodiversity gains. Any off-site biodiversity units relied on by a development must be recorded on the national Biodiversity Gain Site Register, and monitoring schedules should align with what is registered there. Local planning authorities need confidence that off-site gains will be enforceable for thirty years. Guidance stresses the importance of confirming sufficient control over off-site land, especially where the gain sites fall outside the planning authority’s boundary. This is where the responsible body role becomes critical, since they may be the only party able to verify and enforce long-term delivery in certain circumstances. The legal mechanisms that make monitoring enforceable Monitoring is only as strong as the legal agreement behind it. Biodiversity net gain guidance requires that significant on-site gains and all off-site gain sites are legally secured, typically through planning obligations or through a conservation covenant where off-site delivery is involved. The two main types of legal agreements used to secure biodiversity gains are Section 106 agreements & conservation covenants. The legal agreement should reference the management and monitoring plan directly. It should confirm responsibilities for monitoring, reporting frequency, funding for habitat management, and actions required if habitats fail to meet the target condition. Without clear planning obligations or covenant terms, inspectable monitoring becomes difficult, and the statutory biodiversity metric outputs risk becoming theoretical. When statutory biodiversity credits are used, and how they are monitored Statutory biodiversity credits, sometimes referred to as biodiversity credits, are reserved for cases where on-site and off-site gains cannot deliver the required net gain. Government policy is clear that the purchase of statutory biodiversity credits should be a last resort, and monitoring needs to evidence why that route was unavoidable. Where a developer proposes to buy statutory biodiversity credits, local planning authorities should require documentation showing that the gain hierarchy has been followed, that off-site units were not feasible, and that credits will be bought from Natural England. Monitoring then focuses on ensuring the credits are genuinely purchased and reflected in the final biodiversity gain plan approval. Special considerations for irreplaceable habitats and complex sites Irreplaceable habitats cannot be treated like standard habitat change in the biodiversity metric. Monitoring plans should explain how impacts on irreplaceable habitats are avoided or managed. and how any compensatory measures will be verified over time. The same applies to sites with existing protections or with highly distinct habitats that carry a greater risk if condition targets are not met. Linear habitats, such as hedgerows and watercourses, also need careful monitoring because their ecological function depends on continuity and long-term management, not just area-based gains. Resourcing, ecological expertise, and the widening BNG landscape Monitoring BNG requires ecological expertise. Government updates to the small sites metric confirm that an LPA reviewer does not always need to be a qualified ecologist, but authorities still need access to specialist input for complex habitats and high-risk gain plans. Developers and land managers should plan for this by commissioning competent ecologists who understand the statutory biodiversity metric tool and the practicalities of long-term habitat management. Monitoring expectations are also broadening. The Government has proposed extending mandatory BNG to nationally significant infrastructure projects from May 2026. While NSIPs are not yet within the statutory regime, many are already preparing BNG approaches, and monitoring frameworks developed now will underpin delivery in that future landscape. Conclusion Monitoring BNG is the safeguard that turns biodiversity net gain from a calculation into a lasting outcome. It links baseline biodiversity to post-development biodiversity value through measurable habitat creation and habitat enhancement, enforced by clear legal agreement structures and guided by the statutory biodiversity metric. It verifies on-site gains, holds off-site biodiversity units to account through the national register, keeps statutory biodiversity credits as a true last resort, and ensures that biodiversity value is maintained for at least thirty years. Civity supports developers, local planning authorities and land managers in producing monitoring plans that are practical, compliant and evidence-led. Whether your project relies on on-site habitat, off-site gains, or a combination of both, the right habitat management and monitoring approach is what ensures net gain is not just promised but delivered and maintained. DisclaimerThis blog provides a general overview of monitoring biodiversity net gain in England, based on current government and Natural England guidance. It does not constitute legal advice. Monitoring requirements may vary depending on exemptions, phased development, irreplaceable habitats, or the use of off-site units and statutory biodiversity credits. Always confirm project-specific obligations with the relevant planning authority and suitably qualified ecological or legal advisers before finalising a biodiversity gain plan or management and monitoring plan.

Biodiversity net gain is now a legal requirement in England, not an optional aspiration. Since mandatory biodiversity net gain came into force through the Environment Act 2021, local planning authorities have become the delivery engine of a statutory system designed to secure measurable biodiversity gains from development. For most planning permissions, biodiversity net gain is not something that can be “worked out later”. It is embedded in law through a deemed biodiversity gain condition, and it must be satisfied before development can begin. For clients working with Civity, understanding what local planning authorities must do to deliver biodiversity net gain helps reduce planning risk, speed up approvals, and ensure that biodiversity value is genuinely enhanced. This blog explains the duties and practical steps planning authorities must take, aligned with the latest government guidance. The statutory role of local planning authorities The Government’s Biodiversity Net Gain Planning Practice Guidance makes clear that biodiversity net gain (BNG) is mandatory for most Town and Country Planning Act development. The legal framework introduces a deemed biodiversity gain condition on planning permissions granted for development projects within scope. As a result, the relevant local planning authority must approve a Biodiversity Gain Plan before works can commence. This changes local planning profoundly. Authorities are not simply reviewing ecological reports. They must validate baseline evidence, interpret statutory biodiversity metric results, enforce the mitigation hierarchy, and monitor post-development outcomes for at least thirty years. Setting expectations early in the planning process Delivery of biodiversity net gain begins at the planning application stage, where local planning authorities must communicate biodiversity gain requirements clearly. Government guidance expects applicants to show how they will enhance biodiversity and achieve net gain, and authorities should embed these expectations in pre-application advice, validation requirements, and local policy. A key part of this early stage is ensuring that development proposals align with local nature recovery strategies. Authorities should reference any adopted strategy and explain how it informs habitat creation priorities, strategic significance scoring in the biodiversity metric, and wider nature recovery. Local planning authorities should also emphasise the mitigation hierarchy. Applicants must show that they have first avoided impacts on existing habitat, then minimised losses, then sought to create biodiversity on-site through on-site habitat retention, habitat enhancement, and habitat creation. Only after these steps should off-site biodiversity gains be considered, and buying statutory biodiversity credits should be treated as a last resort. Requiring robust baseline evidence within the red line boundary Biodiversity net gain depends on a trustworthy starting point. Local planning authorities must verify that the pre-development biodiversity value has been assessed correctly within the red line boundary of the development site. That means checking that existing habitat has been accurately mapped and classified by habitat type, condition, and distinctiveness, and that surveys follow appropriate seasonal and methodological standards. Authorities may require additional information through their local validation lists, provided these changes are consulted on and published. The purpose is to make sure baseline biodiversity value and biodiversity units are not underestimated, which would distort the entire net gain calculation. Applying the statutory biodiversity metric consistently Local planning authorities must assess applications using the statutory biodiversity metric produced by Defra and Natural England. This metric converts habitats into biodiversity units by considering area, distinctiveness, condition, and strategic significance. Authorities need to interpret metric outputs confidently and challenge assumptions that inflate predicted post-development biodiversity value. This applies equally to major developments and small sites, even where the Small Sites Metric is used. The calculation must still demonstrate that biodiversity net gain requirements will be met and that the post-development biodiversity value exceeds pre-development biodiversity value by at least ten percent after the metric’s risk and time-to-target rules are applied. Determining scope and exemptions Government guidance includes exemptions and transitional arrangements. Local planning authorities must decide, at the validation stage, whether a planning application is subject to mandatory BNG and record this clearly. This is essential for legal certainty. If a development is within scope, the biodiversity gain condition applies. If it is exempt, the authority must make the exemption basis transparent. Approving the Biodiversity Gain Plan before commencement The Biodiversity Gain Plan is the statutory template a developer uses to discharge the biodiversity gain condition. Local planning authorities must review and approve it before any development begins. In doing so, authorities must confirm that the gain plan includes accurate baseline biodiversity value, the final statutory biodiversity metric calculations, a clear explanation of the mitigation hierarchy, and a deliverable package of on-site and, where necessary, off-site biodiversity units. For phased developments, the plan must show how each phase contributes to the overall net gain objective and how biodiversity units will be tracked and secured over time. Scrutinising off-site biodiversity gains and the register Where net gain cannot be achieved entirely on-site, developers may rely on off-site units. Local planning authorities must verify that any off-site biodiversity gains are genuine, additional, and secured for at least thirty years. This includes checking that off-site gain sites are, or will be, recorded on the Biodiversity Gain Site Register operated by Natural England. Authorities should also confirm that off-site biodiversity units meet trading and spatial risk rules and that an appropriate legal agreement is in place with the land manager, whether through a planning obligation or a conservation covenant. Ensuring statutory biodiversity credits remain a last resort. The government explicitly positions statutory biodiversity credits as a last resort. Local planning authorities must ensure that applicants only propose to buy statutory biodiversity credits when on-site habitat measures and off-site gains have been exhausted. Where credits are proposed, authorities should require a clear justification and evidence that the credit purchase will be made through Natural England. This protects the integrity of the biodiversity net gain hierarchy and keeps local biodiversity value uplift central to development. Treating irreplaceable habitat with heightened care Irreplaceable habitat cannot be traded or offset through standard biodiversity units in the same way as other habitats. Local planning authorities must identify whether an irreplaceable habitat is affected, ensure that the statutory biodiversity metric is applied correctly, and require avoidance or bespoke compensation consistent with government guidance. This responsibility is particularly important in sensitive settings where biodiversity net gain interacts with broader aims for green infrastructure, transport network delivery, or strategic local planning priorities. Securing delivery through enforceable legal agreements Authorities must ensure that biodiversity net gain commitments are enforceable. This is typically done through planning obligations under section 106 or through conservation covenants in off-site situations. The legal agreement should lock in the biodiversity gains promised in the gain plan, set out responsibilities for habitat management, define reporting cycles, and establish remedies if net gain delivery fails. Without that legal backbone, net gain becomes a projection rather than a secured outcome. Monitoring post-development outcomes for thirty years Biodiversity net gain is achieved through long-term ecological performance, not simply by passing a metric test. Local planning authorities must therefore require a credible monitoring plan and habitat management approach that runs for at least thirty years. They also need a practical system for reviewing monitoring reports and ensuring compliance. Many authorities are drawing on best practice and support from bodies such as the Planning Advisory Service and the Local Government Association as they build internal frameworks and resourcing for long-term delivery. Preparing for extension to nationally significant infrastructure projects Mandatory BNG currently applies to most TCPA development, but the government has proposed extending a parallel requirement to nationally significant infrastructure projects from May 2026. Local planning authorities and other consenting bodies should build capacity now, because NSIPs will introduce larger schemes where biodiversity net gain must be balanced against major strategic needs. Early preparation will help ensure consistency across the planning system as these changes come into effect. Conclusion Local planning authorities play a defining role in making biodiversity net gain work. They must set expectations early, verify baseline biodiversity value, apply the statutory biodiversity metric consistently, approve the biodiversity gain plan before commencement, scrutinise off-site biodiversity units and the gain site register, and keep statutory biodiversity credits as a genuine last resort. Once planning permissions are granted, they must also secure delivery through enforceable legal agreement structures and ensure compliance through monitoring for at least thirty years. When this system is applied well, it supports the natural environment, strengthens local nature recovery, and enables development that leaves biodiversity better than it found it. Civity supports local authorities, land managers and developers across every stage of this process, from biodiversity metric interpretation to gain plan strategy and long-term habitat management. Disclaimer This blog provides a general overview of what local planning authorities must do to deliver biodiversity net gain in England, based on current government guidance. It is not legal advice. Mandatory BNG includes exemptions, transitional arrangements, and site-specific factors such as irreplaceable habitat or phased development that may alter obligations. Always confirm requirements with the relevant local planning authority and qualified ecological or legal advisers before finalising a planning application or biodiversity gain plan.