Biodiversity Net Gain Report

The Biodiversity Net Gain Report

A biodiversity net gain report is a technical document produced by a qualified ecological consultant that sets out the biodiversity value of a development site before and after development, demonstrates how a minimum 10% uplift in biodiversity will be achieved and provides the evidence base needed to satisfy the mandatory biodiversity net gain requirements under the Environment Act 2021.

Without all the information in a compliant biodiversity net gain report, local planning authorities will not be in a position to make planning decisions for developments that fall within the scope of mandatory biodiversity net gain bng.

The report is not simply a formality; it is the foundation on which the entire biodiversity net gain strategy for a development is built, and the document against which planning officers, consultees and, where relevant, statutory consultees such as Natural England will assess whether the biodiversity net gain bng objective has been met and environmental benefits achieved.

When a Biodiversity Net Gain Report is Required

Mandatory biodiversity net gain has been a legal requirement for most developments in England since early 2024 as a way of mitigating habitat loss and leaving the area in a measurably better state.

The policy is delivered through Schedule 7A of the Town and Country Planning Act 1990, as introduced by Schedule 14 of the Environment Act 2021.

Biodiversity net gain regulations require that every qualifying development leaves the natural environment in a measurably better condition than it was before construction, with biodiversity gains secured for a minimum of 30 years.

The 10% net gain requirement applies to each of the three habitat modules assessed within the statutory biodiversity metric: area habitats, hedgerows and watercourses separately.

Gains from one module cannot be transferred to make up a shortfall in another. This means a development must achieve 10% across all three applicable modules to comply, and the report must demonstrate the on-site gains clearly.

A biodiversity net gain report provides the verified numerical evidence that this requirement for enhancing on site habitats will be met.

It records the pre-development biodiversity unit score, the predicted post-development score, and the measures by which the difference in environmental benefits is achieved.

This data feeds directly into the biodiversity gain plan submitted as a post-consent planning condition, the habitat management and monitoring plan, and any off-site biodiversity gain agreements or statutory credit purchases needed to complete the BNG strategy.

Because the report is the primary technical document on which all subsequent BNG decisions are based, its quality and accuracy are critical.

Errors in the baseline survey, mistakes in the metric calculation or incomplete assessment of habitat condition can undermine the entire BNG submission and lead to queries, delays or refusal from local planning authorities.

Who Does Mandatory BNG Apply To?

Mandatory BNG applies to most new developments in England that require planning permission.

Major infrastructure projects have been subject to the requirement since 12 February 2024. Small sites became subject to it from 2 April 2024. Nationally Significant Infrastructure Projects nsips will be brought within the mandatory regime from 2 November 2026.

Several exemptions currently apply. The main ones are householder applications, developments that affect less than 25 square metres of non-priority habitat or less than 5 metres of non-priority linear habitat, permitted development rights, planning permissions granted before the relevant mandatory date, temporary permissions of five years or less and certain Crown and national security developments.

A new area-based exemption for sites of 0.2 hectares or below is proposed to take effect from 31 July 2026, subject to parliamentary scheduling.

If introduced, the government estimates this will remove approximately 50% of currently non-exempt residential planning applications from the scope of mandatory BNG.

The existing self-build and custom-build exemption is proposed to be removed at the same time, on the basis that most such projects would fall within the 0.2 hectare threshold.

A further consultation on a potential brownfield residential exemption for sites of up to 2.5 hectares closed on 10 June 2026, and its outcome is not yet confirmed.

The position on exemptions continues to evolve, and current government guidance on GOV.UK should always be checked before drawing conclusions about whether a specific development is exempt.

What Does a Biodiversity Net Gain Report Cover?

A biodiversity net gain report contains several interconnected components, each of which contributes to the overall assessment of whether and how the 10% BNG requirement will be met to fulfil planning obligations and enable nature recovery.

Ecological Baseline Survey 

The starting point for any BNG report is a thorough survey of the existing wildlife habitats on and immediately around the proposed site’s red line boundary.

An ecological consultant will visit the site and assess every habitat present, recording its type, extent, condition and ecological distinctiveness using the UK Habitat Classification system. The condition of each habitat is assessed against the standardised criteria published alongside the statutory biodiversity metric.

Where priority habitats or wildlife habitats classed as irreplaceable are found, such as ancient woodland, open mosaic habitat, lowland meadow or blanket bog, additional considerations apply, as these habitats cannot be offset through the standard metric and must be addressed through bespoke compensation.

The survey data is entered into the statutory biodiversity metric tool to generate the pre-development biodiversity unit score across all three modules. This score forms the baseline against which the required 10% increase is calculated.

Impact Assessment

The consultant will review the development proposals in detail to establish their effect on existing habitats.

This involves assessing which habitats will be wholly or partially lost to construction, which will be retained, and whether any retained habitats are likely to decline in condition as a result of disturbance or changed management.

The impact assessment produces a picture of the development’s effect on biodiversity before any enhancement measures are applied.

Post-Development Biodiversity Metric Calculation

The proposed habitat creation and enhancement measures, including all landscaping, planting, green infrastructure and ecological features forming part of the scheme design, are entered into the statutory biodiversity metric tool as post-development habitat parcels.

The tool calculates the post-development unit score, taking into account the type, area, target condition, time to target condition and spatial factors of each proposed habitat. The difference between the pre-development and post-development scores, expressed as a percentage, must be at least 10% across each applicable module.

The statutory biodiversity metric, published by DEFRA and originally developed by Natural England, currently at version 1.0.3, scores habitats across four key variables: distinctiveness, condition, strategic significance and connectivity.

Trading rules apply throughout: habitats of higher distinctiveness must be replaced with habitats of the same or higher type.

The spatial risk multiplier within the metric applies a discount to gains delivered away from the development site, incentivising on-site and locally delivered habitat creation.

Mitigation and Compensation Strategy

The biodiversity net gain report sets out how the project will follow the biodiversity gain hierarchy.

The mitigation hierarchy involves seeking to avoid harm to biodiversity through design decisions, then minimising unavoidable harm, then restoring or enhancing habitats on site, then compensating for residual losses through off-site provision.

The report must demonstrate that this hierarchy has been applied and that the land management strategy for achieving the 10% target follows it in the correct order. 

For minor developments specifically, from 31 July 2026, off-site biodiversity gains will carry equal weight to on-site habitat creation in the hierarchy.

This change is a practical acknowledgement that small-scale, self-build sites – particularly urban infill plots – often have genuinely limited scope for meaningful on-site habitat creation.

For major developments, on-site delivery continues to take priority.

On-Site and Off-Site Provision

There are three methods of providing bng. Where on-site habitat creation and enhancement is sufficient to achieve the 10% target across all three modules, the report will confirm this and set out the details of the proposed habitat works.

Where it is not sufficient, the shortfall must be made up using registered off-site biodiversity units purchased from a habitat bank listed on the Natural England biodiversity gain site register. Units must be registered before they can be allocated to a development.

A spatial risk multiplier discount applies to off-site gains relative to the distance of the habitat bank from the development site, with the exception of some NSIP off-site gains within the same local authority or national character area.

Where neither on-site nor off-site solutions can enhance biodiversity and close the gap, statutory biodiversity credits purchased from Natural England may be used as a last resort.

Statutory credits are priced at a deliberate premium to incentivise real habitat delivery in preference to financial mitigation.

Irreplaceable Habitats

Where irreplaceable habitats are present on a site, these must be recorded in the metric tool but cannot be offset through the standard calculation.

Any loss or deterioration of an irreplaceable habitat is governed by the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024, which require bespoke compensation to be agreed separately.

The biodiversity net gain report must identify all irreplaceable habitats clearly and address the compensation requirements for biodiversity losses accordingly.

The Statutory Biodiversity Metric

The statutory biodiversity metric is the mandatory calculation tool that must be used for all BNG assessments for developments requiring planning permission in England.

No other metric or methodology is acceptable for the purposes of demonstrating mandatory BNG compliance.

It is an Excel-based tool, published by DEFRA, and must be completed by a competent person – someone with the ecological knowledge to identify and assess habitats accurately, understand the management requirements for habitats to be created or enhanced, and apply the metric rules correctly.

The metric operates in three separate modules: area habitats, hedgerows and watercourses. As noted above, the 10% requirement must be achieved in each module independently. A strong performance in one module does not compensate for a shortfall in another.

A Small Sites Metric (SSM) is available as a simplified alternative for eligible developments. This applies to residential developments of one to nine dwellings on sites of one hectare or less, or where the number of dwellings is unknown, sites of under 0.5 hectares.

The SSM cannot be used where priority habitats are present on the site, where protected species have been recorded or where off-site mitigation is needed to meet the target.

The SSM follows the same Excel format as the main metric but involves a shorter and less detailed assessment process, reflecting the lower complexity of small site developments.

The statutory biodiversity metric user guide, updated in July 2025, sets out the rules and principles governing how the tool must be used, including the habitat trading rules, the approach to assessing individual trees, guidance on strategic significance and the treatment of habitats created in advance of development.

The Difference Between a BNG Report and a Biodiversity Gain Plan

These two documents are closely related but are not the same. 

A biodiversity net gain report is the primary technical document produced by the ecological consultant. It contains the baseline survey results, the metric calculations and all the technical evidence demonstrating how the 10% requirement will be met.

It is typically prepared and submitted alongside the planning application, or at least before the application is determined.

A  biodiversity gain plan is a separate statutory form published by DEFRA. It is submitted after planning permission has been granted, as a discharge of the pre-commencement BNG condition attached to the consent.

Planning authorities have eight weeks to approve or refuse it. The biodiversity gain plan summarises the BNG strategy confirmed in the report and references the legal mechanisms, such as a Section 106 agreement or conservation covenant, through which the gains are secured for 30 years.

Both documents are required for most developments subject to mandatory BNG. In practice, the biodiversity net gain report contains the substance; the biodiversity gain plan is the formal mechanism for confirming compliance and discharging the condition.

Preparing both through a single commission with the same ecological consultant is the most efficient approach.

Getting Your Biodiversity Net Gain Report

A BNG report must be prepared by a qualified ecological consultant with experience of the statutory biodiversity metric.

The process begins with an ecological baseline survey, which must be carried out at a time of year appropriate for the habitats present on site. Where the site has complex or sensitive habitats, additional specialist surveys may be required before the baseline can be established.

Engaging a BNG consultant early, ideally before the scheme design is fixed, gives the project team the best opportunity to assess all the information and integrate habitat enhancement into the development layout to achieve the most positive effects from the outset.

By identifying the most cost-effective route to deliver bng, you will avoid the policy becoming a last-minute obstacle to the start of construction,

Use our free service to get fast, no-obligation quotes from trusted BNG consultants in our network to help you fulfil your planning obligations and reduce your scheme’s environmental impact.

Fill in the form at the top of this page, and we will connect you with a specialist who can assess your site, carry out the biodiversity metric calculations and produce a compliant report to support your application.