What Is Biodiversity Net Gain Planning?

For years, most developers paid little heed to the ecological impact of their projects. They came, they built, and they moved on to the next site. All that changed in February 2024, when biodiversity net gain (BNG) became a condition of planning permission in England.¹

BNG requires developers to leave their sites in a better condition than they found them by a factor of at least 10%. While some schemes are exempt from biodiversity net gain planning (you can find them listed here), those that aren't must now follow a detailed roadmap to meet the legal threshold.

The benefits of a robust biodiversity net gain plan are twofold: Not only does it help secure planning permission, but it also protects any enhanced habitats for at least 30 years.

This guide will explain the biodiversity net gain planning process, including examining the legal basis for BNG, what a biodiversity gain plan should include, the biodiversity hierarchy, and what local planning authorities expect to see before giving projects the green light.

Biodiversity Net Gain: The Legal Basis

The Environment Act 2021 inserted new provisions into the Town and Country Planning Act 1990,² establishing the biodiversity gain objective as a condition attached to planning permissions in England.³

It became a legal requirement in February 2024 for most developments, while nationally significant infrastructure projects must comply with the minimum 10% uplift in BNG from 2 November 2026.⁴

By March 2026, some local councils in England had implemented biodiversity policies with a 20% threshold, while others were aiming for a 30% limit.⁵ However, in August, the government issued a new National Planning Policy Framework⁶ which pushed back on efforts to demand a higher BNG requirement.

It said: "Development plans should only set local standards for biodiversity net gain which are in excess of the statutory net gain requirement where this is for specific site allocations, and is fully justified and deliverable." The NPPF also noted that local standards could not be extended to developments which are exempt from statutory BNG.

How to Demonstrate Biodiversity Net Gain

So how do developers go about achieving the required minimum 10% improvement in habitat when designing their projects?

First and foremost, developers should avoid any impact on habitats that have medium, high or very high distinctiveness. For those sites, and all onsite habitats affected by major projects, developers must adhere to the biodiversity hierarchy.⁷

It requires on-site enhancements or restoration to be the first priority, followed by the purchase of off-site BNG solutions. It should be noted these BNG units become more expensive the further away they are from the original development site.

From August 2026,⁸ developers of minor projects (those bigger than 0.2 hectares but which don't meet major development criteria) can opt for off-site biodiversity units immediately. It comes after regulatory changes⁹ gave them equivalence with on-site enhancements in the biodiversity hierarchy.¹⁰

In circumstances where the minimum 10% biodiversity net gain cannot be achieved through on- or off-site solutions, and all possible avenues have been exhausted, developers can offset their project's impact by buying statutory biodiversity credits from the government.

The biodiversity hierarchy should not be confused with the mitigation hierarchy¹¹ laid out in the National Planning Policy Framework.¹² It states that: "If significant harm to biodiversity resulting from a development cannot be avoided (through locating on an alternative site with less harmful impacts), adequately mitigated or, as a last resort, compensated for, then the development should be refused."

If a development impacts an irreplaceable habitat, it is explicitly excluded from BNG. Instead a bespoke compensation package must be agreed with the local planning authorities. These situations are dealt with on a case-by-case basis.¹³

The Biodiversity Gain Plan and the Planning Application Process

If a developer believes their project would trigger the mandatory BNG requirement, they must submit several documents after planning permission has been granted.¹⁴ Arguably the most important of these is the biodiversity gain plan.

It should be submitted in writing to the relevant planning authority as soon as one day after planning permission has been granted (but no earlier).¹⁵ Developers are encouraged to use this template to ensure all the required information¹⁶ is in one place. Among the details the biodiversity gain plan should include are:

• efforts to minimise the development's impact on the biodiversity of the on-site or any other habitat within the site's red line boundary
• details of any irreplaceable habitats present and any compensation plans
• the on-site habitat's pre-development biodiversity value*
• the on-site habitat's post-development biodiversity value to establish any losses*
• evidence the biodiversity net gain hierarchy has been followed
• any registered off-site biodiversity gain units allocated to the development
• any biodiversity credits purchased for the development
• a detailed habitat management and monitoring plan (HMMP) covering the required, minimum 30-year period¹⁷

*The statutory biodiversity metric tool should be used by a competent professional to calculate the pre- and post-development biodiversity values needed for the biodiversity gain plan. The tool will also calculate the number of units required to meet the minimum 10% threshold.

Phased Developments

Although biodiversity gain plans for phased developments cover the same ground, there are some special arrangements and they require separate templates.

An overall biodiversity gain plan must be submitted to and approved by the planning authority before any development can begin. This lays out the framework for how the biodiversity gain objective of at least a 10% gain is expected to be met across the multi-phase development.

After that, successive biodiversity gain plans for each phase must be submitted to and approved by the planning authority before the development of that phase can begin. They also document the progress towards the overall biodiversity gain goal for the project, once clear proposals for each phase have been developed.¹⁸

In most cases, the local planning authority that granted planning permission will be the one to approve the biodiversity gain plan, enabling development work to begin. There are circumstances under which the decision maker granting planning permission is not the local planning authority. They can be found here.

The Role of Local Planning Authorities in BNG Planning

Local planning authorities play a central role throughout the biodiversity net gain planning process. They are responsible for checking that submitted biodiversity gain plans meet the statutory requirements, and that biodiversity metric calculations have been correctly applied.¹⁹

LPAs must also be satisfied that proposed legal agreements covering off-site biodiversity net gain units - whether they are covered by a section 106 agreement or a conservation covenant - will meet the minimum 10% threshold.²⁰ The local planning authority will also determine if the BNG trading rules have been met, and ensure any BNG units are of the same calibre as the damaged or lost habitat.²¹

Local Nature Recovery Strategies and BNG

Regulatory changes that put on- and off-site BNG enhancements on an equal footing for smaller developments²² were among several changes confirmed in 2026 by Defra, but which, at the time of writing, had no publication date.²³

They included adjusting how spatial risk would be assessed for area habitats, using solely Local Nature Recovery Strategy areas²⁴ instead of the current method of local planning authority (LPA) and National Character Area boundaries.

In its government response to the previous year's consultation, published in April 2026, Defra said the change would apply to all types of development and "increase flexibility for off-site BNG and better align with future local government reorganisation".²⁵

How Much Does a Biodiversity Gain Plan Cost?

The cost of preparing a biodiversity gain plan, including the underlying ecological surveys and statutory biodiversity metric calculations, varies greatly.

A site with straightforward, modified habitats will be less expensive than one that is a complex mosaic, including potential priority or irreplaceable habitats that demand more detailed survey work.

Contacting an experienced ecologist at an early stage - ideally before submitting a planning application - allows developers to understand likely costs, and determine potential on- and off-site biodiversity net gain requirements, before committing to a particular design.

How We Support BNG Planning

We work with developers across England to navigate the practicalities of biodiversity net gain planning, from initial site assessment through to discharge of the biodiversity gain condition, and long-term habitat management.

For developers preparing a biodiversity gain plan, we provide on-site mitigation design support, identifying practical opportunities for habitat creation within the development site boundary.

In almost every case, this design work can reduce a development's overall biodiversity deficit, reducing the number of units that need to be bought and improving a development's overall viability.

For developers who need off-site BNG units, our national network of registered offsite biodiversity gain sites means BNG units can be secured within a relevant National Character Area in weeks rather than months, helping to keep planning applications and development programmes on track.

Whether you are working through your first biodiversity gain plan or managing a complex, phased development across multiple local planning authority areas, we can help.

Expert Help at Every Stage of the BNG Planning Process

Our team understands what local planning authorities expect to see, having contributed directly to Natural England's technical guidance on related nature-based mitigation approaches.

This depth of regulatory understanding means we can help developers avoid common pitfalls that lead to delay at the planning permission stage.

If you are preparing a planning application and need support with your biodiversity gain plan, statutory biodiversity metric calculations, or sourcing off-site BNG units, get in touch.

Email us at sales@greenshank-environmental.com or fill in this contact form and we'll be in touch as soon as possible.