Defra revises England's biodiversity net gain regime following twin consultations

The Department for Environment, Food and Rural Affairs (Defra) has set out significant changes to England's biodiversity net gain (BNG) framework, with further changes to be implemented later this year following two separate consultation responses published in April. 

The BNG policy was implemented under the Environment Act 2021. Most developments in England that require planning permission under the Town and Country Planning Act 1990 (TCPA) have been within scope of the policy since April 2024. 

The core requirement of BNG is to ensure that projects leave the natural environment in a better condition than before the work began, delivering at least a 10% gain in biodiversity compared to the pre-project baseline. The 10% gain must be maintained for at least 30 years. BNG rules include various technical mechanisms to determine baseline biodiversity and the "value" which is attributed to certain types of biodiversity.

Following consultation, Defra published its two separate responses in April covering minor changes to exemptions, BNG for brownfield sites and other improvements and BNG application for nationally significant infrastructure projects (NSIPs). 

New exemptions 

Defra's consultation responses confirmed the exemption of developments of 0.2 hectares or less (a policy first announced in December 2025). The consultation also suggested there may in future be changes to the de minimis exemption to account for, among other things, change of use applications or installation of solar panels on industrial buildings. 

There will also be new exemptions for development whose primary objective is to conserve or enhance biodiversity; temporary planning permissions covering permissions granted for a maximum of 5 years; and development enhancing parks, playing fields and public gardens. 

Secondary legislation introducing these changes will come into force on 6 August. 

In an effort to streamline the BNG system, particularly for smaller developers, Defra will introduce a new digital, integrated service for BNG, replacing the existing Excel metric tool.

Offsite and brownfield

Further updates include the biodiversity gain hierarchy for minor developments will be amended so that off-site biodiversity gains are as preferable as the enhancement and creation of on-site habitat.

A spatial risk multiplier (SRM) will also be based on local nature recovery strategy areas, instead of, as is currently the case, local planning authority (LPA) and national character area (NCA) boundaries. These new areas will be significantly larger than existing LPA areas, so it is expected that the options for off-site BNG will increase without developers being penalised by the requirement to apply the SRM.

Brownfield developments with "open mosaic habitat" (OMH) will also benefit from the introduction of OMH identification criteria and improvements to the metric information for that habitat. There will also be reviews of other urban habitat types to create a more accurate metric representation of urban habitats.

Since the consultation, Defra has issued a further consultation on the BNG exemptions for residential brownfield sites. The consultation closed on 10 June. The government is yet to confirm when the response to this consultation will be published. 

Infrastructure projects

From 2 November 2026, BNG rules will apply to all NSIP applications irrespective of project type, with no exemptions or voluntary approaches permitted. BNG will not apply to any changes to development consent orders (DCOs) where the original DCO was not already subject to mandatory BNG. 

The SRM will in most instances not apply where an NSIP crosses multiple LPAs, NCAs or marine plan areas and off-site BNG units are allocated within only one of those areas. Watercourse units are an exception, due to their ecological importance.

Defra has confirmed that unimpacted habitats do not need to be included in the BNG baseline before a project begins, and that the baseline is to be calculated at the time of submitting the biodiversity gain plan, rather than at the time of the NSIP application. 

BNG requirements will apply to areas of "temporarily acquired" land, which will be returned to owners following the completion of a project. For habitats of low and very low distinctiveness, this will be accompanied by a change to timescales for temporary impacts from two years to five years before they are considered "retained". The change is intended to incentivise the use of the least ecologically valuable habitats for temporary works.

In an instance of diversion from the TCPA system, NSIPs will not have to prioritise on-site BNG before considering off-site alternatives. This is on the basis that the scale of these large infrastructure projects creates the potential to produce better ecological outcomes through strategic delivery that may involve off-site gains.

Defra has published a series of biodiversity gain statements that set out how developers of NSIPs must calculate, deliver and report on the project's BNG. The statements are broken down by project type, with an additional statement for projects where no project-specific statement has been published. 

Osborne Clarke comment

BNG has now been part of the planning process for over two years and is beginning to gain real traction. The government has shown, through its willingness to consult and amend BNG, that it remains committed to the policy, including by broadening BNG's application to NSIPs from November. 

One likely impact of the changes introduced following these two consultations is to bolster the off-site BNG market, which will help to ensure that market remains buoyant and continues to grow, offering opportunities to those able to generate off-site biodiversity units on their land.

Developers will need to continue to consider BNG at an early stage of their development planning process as further legislation and guidance are expected in the months ahead.

Adam Budd, a trainee solicitor with Osborne Clarke, contributed to this Insight.