Biodiversity net gain (BNG) is now a central requirement within the English planning system, requiring most development projects to deliver at least a 10% increase in biodiversity value. While the principle is consistent, the delivery of biodiversity net gain can take two distinct forms: on-site biodiversity net gain within the development site or off-site biodiversity units secured elsewhere.
Understanding the difference between BNG off-site credits and on-site biodiversity net gain is essential for developers, land managers and planning professionals seeking to meet biodiversity net gain requirements efficiently and compliantly.
The Policy Context and Legal Framework
Mandatory biodiversity net gain is established under the Environment Act 2021 and supported by detailed policy and technical guidance.
All biodiversity gains must be calculated using the statutory biodiversity metric, developed by Natural England and available through the statutory biodiversity metric tool and guidance.
Local planning authorities are responsible for ensuring that development proposals meet the biodiversity gain objective, typically through the submission and approval of a biodiversity gain plan.
What Is On-Site Biodiversity Net Gain?
On-site biodiversity net gain refers to habitat creation, habitat enhancement and biodiversity improvements delivered within the red line boundary of the development site.
This approach focuses on enhancing on-site habitats as part of the development design. Examples include green infrastructure, tree planting, restoring natural habitats or improving existing habitat conditions to increase biodiversity units.
The biodiversity metric tool is used to calculate baseline biodiversity value and model post-development biodiversity value. Developers must demonstrate that on-site gains contribute meaningfully to achieving biodiversity net gain to include them within their calculations; this usually involves securing their ongoing management and maintenance via a Section 106 agreement for at least 30 years.
On-site delivery aligns closely with the mitigation hierarchy, which prioritises avoiding and minimising biodiversity loss before considering compensation. As a result, local planning authorities expect significant on-site gains wherever feasible.
What Are BNG Off-Site Credits?
BNG off-site credits, more accurately described as off-site biodiversity units, are biodiversity gains delivered outside the development site. These units are generated through habitat creation or restoration on separate land, often referred to as habitat banks or gain sites.
Off-site biodiversity gains must be legally secured for at least 30 years and registered on the statutory register maintained by Natural England. The operation of this system is explained within the biodiversity gain site register guidance.
Developers may purchase biodiversity units from these sites to compensate for any shortfall in on-site biodiversity net gain. The units are then allocated to the development and recorded as part of the biodiversity gain plan.
The Role of the Biodiversity Gain Hierarchy
The biodiversity gain hierarchy governs how biodiversity net gain should be delivered. It requires developers to prioritise on-site habitat enhancement before relying on off-site solutions.
This hierarchy reflects the broader mitigation hierarchy within planning policy, ensuring that biodiversity loss is first avoided as the preferred approach, then minimised within the development site before, finally, compensation is considered.
Local planning authorities will scrutinise biodiversity gain plans to ensure that off-site gains are not used prematurely or in place of achievable on-site improvements.
When Are Off-Site Units Used?
Off-site biodiversity units are typically required where the development site has limited capacity to deliver sufficient biodiversity gains. This may occur in high-density urban developments, constrained sites or schemes involving significant habitat loss.
In these cases, off-site solutions allow developers to achieve biodiversity net gain by investing in habitat creation elsewhere. Off-site habitats may deliver greater ecological value where they are strategically located, larger in scale, or aligned with Local Nature Recovery Strategy priorities.
The statutory biodiversity metric applies spatial multipliers, meaning that units located within the same local planning authority area or in proximity to the development site are more valuable.
Statutory Biodiversity Credits as a Last Resort
Where neither on-site gains nor off-site biodiversity units are available, developers may buy statutory biodiversity credits from the government.
These credits are intentionally priced higher than market-based off-site units to encourage private habitat creation and restoration. Their use is restricted to situations where other options have been exhausted, as outlined in the statutory biodiversity credits framework.
Comparing On-Site and Off-Site Approaches
On-site biodiversity net gain offers clear advantages in terms of integrating biodiversity into development design, supporting local ecosystems and aligning with planning policy expectations. It also reduces reliance on external agreements and simplifies long-term governance, where appropriately managed.
However, on-site delivery is often constrained by site viability, land availability and competing development priorities.
Off-site biodiversity net gain provides flexibility, allowing developers to secure biodiversity units from dedicated habitat banks designed specifically to deliver ecological value. These sites can deliver biodiversity improvements at scale and contribute to wider environmental objectives.
The most effective biodiversity net gain delivery strategies often involve a combination of on-site gains and off-site gains, ensuring compliance with the biodiversity gain hierarchy while achieving the required net gain efficiently.
Legal and Long-Term Considerations
Both on-site and off-site biodiversity gains must be secured through legal agreements and supported by a monitoring plan lasting at least 30 years.
Off-site units are typically secured through conservation covenants or section 106 planning obligations. Government guidance on conservation covenants is available through the conservation covenant framework.
Local authorities and responsible bodies oversee compliance, ensuring that habitat enhancement works are delivered and maintained over time.
Strategic Decision-Making for Developers
Choosing between on-site and off-site biodiversity net gain requires a detailed understanding of the development site, baseline biodiversity value and planning constraints.
Early engagement with ecologists and planning professionals is essential to identify the most effective approach. Developers should model different scenarios using the biodiversity metric to determine the optimal balance between on-site habitat enhancements and off-site solutions.
Consideration should also be given to programme timelines, cost, land ownership constraints and the availability of suitable off-site units within the relevant local planning authority area.
Expert Support for BNG Delivery
Delivering biodiversity net gain in compliance with current regulations requires technical expertise in biodiversity metric calculations, legal structuring and habitat management.
At Civity, we facilitate the delivery of compliant biodiversity net gain by providing access to pre-registered off-site biodiversity units from our land bank.
We work with landowners to bring forward biodiversity gain sites and secure them through the appropriate legal agreements and registration processes. For developers, we review submitted biodiversity metrics, identify unit requirements, and allocate suitable off-site units in line with statutory trading rules.
We can also support the completion of relevant sections of the Biodiversity Gain Plan, working alongside the project ecologist where required.
Disclaimer
This article is intended for general informational purposes and reflects the biodiversity net gain framework in England at the time of writing. It does not constitute legal, ecological or planning advice. Developers and landowners should seek professional advice tailored to their specific circumstances and refer to current government and Natural England guidance to ensure compliance with evolving biodiversity net gain regulations.
