Biodiversity Gain Plan

What is a Biodiversity Gain Plan? 

A biodiversity gain plan is a formal document submitted to a local planning authority after planning permission has been granted.

It sets out precisely how a development will meet its mandatory biodiversity net gain (BNG) requirement, demonstrating the pre-development biodiversity value of the site, explaining how a minimum 10% uplift will be achieved, and confirming the legal mechanisms through which those gains will be secured for a minimum of 30 years.

The biodiversity gain plan is a statutory requirement under Schedule 7A of the Town and Country Planning Act 1990, as inserted by Schedule 14 of the Environment Act 2021.

When planning permission is granted for a development subject to mandatory biodiversity net gain, it will automatically include a pre-commencement condition requiring a biodiversity gain plan to be submitted and approved before any work can begin on site. The relevant local planning authority has eight weeks to approve or refuse it.

The Department for Environment, Food and Rural Affairs (DEFRA) has published a standard template for the biodiversity gain plan, which must be completed by a qualified ecological consultant.

It cannot be filled in by the developer alone: the biodiversity metric calculations and habitat assessments underpinning it require specialist ecological expertise to verify how a site will achieve biodiversity net gain.

Biodiversity Net Gain Policy: The Background

Mandatory biodiversity net gain has applied to most development in England since early 2024 as part of the National Planning Policy Framework.

Major developments have been subject to the requirement from 12 February 2024, and smaller sites from 2 April 2024.

Biodiversity net gain requirements mean that when a development takes place, the biodiversity value of the natural environment is left in a demonstrably better state than it was before construction began.

The minimum statutory requirement is a 10% net gain in biodiversity value, measured according to DEFRA’s current biodiversity metric tool calculation.

The metric is a spreadsheet-based calculation tool for measuring biodiversity that converts habitat types, areas, conditions and locations into standardised biodiversity units.

Calculating biodiversity net gain involves establishing a pre-development score through a baseline survey of the site: a biodiversity net gain assessment.

The post-development score is calculated from the proposed habitat enhancements and other biodiversity improvements. The difference between the two, expressed as a percentage, must be at least 10%.

A simplified Small Sites Metric (SSM) is available for smaller development sites: broadly those involving one to nine residential dwellings on a site under one hectare, or non-residential developments under 1,000 square metres or one hectare.

The SSM cannot be used where priority habitats are present on the site or where protected species have been recorded.

Nationally Significant Infrastructure Projects (NSIPs) will be brought within the mandatory biodiversity net gain regime from 2 November 2026.

The Difference Between a Biodiversity Gain Plan and a Biodiversity Net Gain Plan

These two documents are closely related but serve different functions, and the distinction matters.

A biodiversity gain plan (BGP) is the specific statutory form published by DEFRA. It is submitted post-consent as a planning condition and must be approved by the relevant local planning authority before development can start.

Its purpose is to confirm, in a standardised format, how the development will meet the biodiversity gain objective and secure measurable net gains.

Not all local authorities will require one to be submitted at the application stage, but all developments subject to mandatory biodiversity net gain will need one approved before construction begins to comply with biodiversity net gain regulations.

A  biodiversity net gain plan, (BNG plan) is a broader, more detailed document that forms part of the planning application itself, setting out how biodiversity net gain requirements will be met.

It records the results of the biodiversity metric calculation, sets out the ecological baseline of the site, explains the proposed approach to wildlife habitats in terms of enhancement and creation, identifies whether on-site gains achieved on site are sufficient or whether off-site provision is needed, and establishes the overall strategy for achieving and securing net gain. It is typically submitted alongside the planning application rather than as a post-consent condition.

Both documents are a legal agreement required for most developments subject to mandatory biodiversity net gain relating to current and future developments.

The biodiversity net gain plan supports the planning application; the biodiversity gain plan discharges the planning condition once permission has been granted.

What Does a Biodiversity Gain Plan Include? 

The DEFRA biodiversity gain plan template is structured to capture all the information that corresponding local planning authorities need to assess whether the biodiversity gain condition has been satisfied.

A completed biodiversity gain plan will cover the following:

Baseline Biodiversity Assessment 

This section records the biodiversity value of the site before development, established through an ecological baseline survey or preliminary ecological appraisal.

The surveyor will assess all habitats present within the red line boundary and proxy habitat, including their type, area, condition and ecological features such as irreplaceable habitat sites, ancient woodland and areas of local importance.

Particular attention is given to important habitats and protected wildlife species, which are subject to additional protections and cannot simply be offset through the standard biodiversity metric.

The baseline data is entered into the statutory biodiversity metric tool to generate the pre-development biodiversity unit score.

Three Methods for Providing Biodiversity Enhancements

This section sets out how the development will deliver the required 10% net gain.

It lists measures for enhancing on-site habitats, habitat creation and other enhancement measures proposed on site, such as the establishment of wildflower meadows, native tree and shrub planting, wetland features, green roofs, hedgerow creation or the improvement of existing natural habitats in poor condition or degraded habitats.

Where on-site measures alone are insufficient to achieve the 10% target, the plan will identify the off-site biodiversity units required to make up the shortfall, including the purchase of biodiversity units from an off-site habitat bank that may be identified via the biodiversity gain sites register, or the last resort may be to buy statutory biodiversity credits from Natural England.

The Biodiversity Gain Hierarchy for Environmental Net Gain

Developers must follow the biodiversity gain hierarchy when demonstrating how biodiversity net gain will be achieved. The hierarchy requires that avoiding harm to biodiversity is always considered first.

Where harm cannot be avoided, on-site habitat enhancement and creation takes priority.

Off-site registered gains are the next option, followed by statutory credits as the final resort. The biodiversity gain plan must demonstrate that this hierarchy has been followed.

Local planning authorities are required to have regard to the hierarchy when deciding whether to approve a submitted plan.

Biodiversity Metric Calculations

The completed statutory biodiversity metric spreadsheet must accompany the biodiversity gain plan.

A summary of the calculations is not sufficient: the full Excel spreadsheet must be submitted so that the local planning authority can verify that the calculations have been carried out correctly and that the post-development score exceeds the pre-development score by at least 10%.

Legal Mechanisms for Securing Gains

Biodiversity gains must be secured for a minimum of 30 years. The biodiversity gain plan must confirm the legal instrument through which this will be achieved.

The main options are a Section 106 planning obligation, a conservation covenant registered with a responsible body approved by DEFRA, or a combination of both.

Where off-site gains are being used, the relevant off-site biodiversity gain agreement must also be referenced and evidence of registration on the Natural England biodiversity net gain register included.

Habitat Management: Ongoing Management and Monitoring Plan

For most developments involving new habitat creation or enhancement, a  Habitat Management and Monitoring Plan (HMMP) will be required as part of or alongside the biodiversity gain plan.

The HMMP sets out how the habitats created or enhanced through the development will be managed and maintained over the 30-year securing period, the monitoring regime that will be used to assess their condition, and the performance reviews that will be carried out at agreed intervals to confirm that habitats are developing as intended, maintaining overall biodiversity value.

Stakeholder Engagement and Wider Policy Context

The biodiversity gain plan should reference any relevant pre-application discussions with the local planning authority, the local nature recovery strategy for the area, and any other policy considerations that have informed the biodiversity net gain approach, including alignment with Local Plan policies, green infrastructure strategies and any site-specific requirements relating to protected species or designated sites.

Phased Developments

Where a development is to be carried out in phases, an overarching biodiversity gain plan covering the entire scheme must be submitted alongside a separate phased biodiversity gain plan for each individual phase.

Each phased plan must demonstrate how that phase contributes to the overall biodiversity net gain target for the development.

Who can be Subject to Mandatory Biodiversity Net Gain? 

Mandatory biodiversity net gain applies to a wide range of development types.

Local authorities can request a biodiversity gain plan for any development to which the biodiversity net gain requirement applies, including:

• Residential developments of all scales, from single dwellings to large housing estates, where not exempt.
• Commercial, industrial and mixed-use schemes.
• Brownfield site redevelopments.
• Infrastructure and public realm projects.
• Change of use applications involving physical works that affect habitat.
• Agricultural developments where the biodiversity net gain regime applies.
• Renewable energy projects.
• Educational and healthcare facilities.
• Urban green space and landscaping projects.

The requirement also applies where a development site overlaps with or is adjacent to statutory protected sites or designated areas, including Sites of Special Scientific Interest (SSSIs), Local Nature Reserves, Areas of Outstanding Natural Beauty and National Parks.

Current Exemptions from Mandatory Biodiversity Net Gain

Not all developments are subject to the mandatory biodiversity net gain requirement.

The current exemptions include:

• Householder applications (home extensions, conservatories and similar works).
• Developments falling below the de minimis threshold – broadly those affecting less than 25 square metres of non-priority habitat, or less than 5 metres of non-priority linear habitat.
• Planning permissions that applied before 12 February 2024.
• Developments with temporary planning permission of five years or less.
• Sites being developed specifically to deliver biodiversity net gain for another scheme.
• Certain Crown and national security developments.
• Developments forming part of or ancillary to the high-speed rail network.

An area-based exemption for sites of 0.2 hectares or below is proposed to take effect from 31 July 2026.

This has not yet been implemented: it remains a proposal confirmed in the government’s response to the biodiversity net gain consultation published on 15 March 2026, and the position should be verified before any reliance is placed on it.

If introduced, it is expected to remove a significant proportion of smaller residential applications from the scope of mandatory biodiversity net gain.

A related proposal to remove the existing self-build and custom-build exemption, on the basis that the 0.2 hectare rule would capture most such dwellings, is also proposed for the same date.

Because the exemption position has evolved since biodiversity net gain was first introduced and continues to develop, it is important to check the current government guidance on GOV.UK when assessing whether a specific development is exempt.

Obtaining a Biodiversity Gain Plan

A biodiversity gain plan must be prepared by a qualified ecological consultant with experience of the statutory DEFRA biodiversity metric and the mandatory biodiversity net gain framework.

The process begins with an ecological baseline survey of the site to establish the biodiversity unit score before development, followed by metric calculations and the development of a habitat enhancement strategy.

Where the local planning authority requires a biodiversity net gain plan at the application stage as well as a biodiversity gain plan post-consent, both can be prepared as part of the same commission.

Engaging a biodiversity net gain consultant early, ideally at pre-application stage, gives a development team the best chance of integrating the BNG strategy into the scheme design from the outset, identifying opportunities for on-site gains that reduce reliance on more costly off-site provision.

As well as complying with legal requirements to leave a site in a measurably better state, the advice of a consultant will avoid the risk of BNG becoming a last-minute obstacle to the start of construction.

If you own land or aim to develop a site, use our free service to get fast, no-obligation quotes from trusted biodiversity net gain consultants in our network.

Fill in the form at the top of this page, and we will connect you with a specialist who can provide further information and ensure that you comply with biodiversity net gain policy.

They will be able to handle your biodiversity gain plan, metric calculations and supporting documentation, and provide further guidance to help keep your development proposal on track through the planning process.