Biodiversity Net Gain (BNG) is now mandatory for major developments in England. We outline the terminology, tools, metrics and guidance developers should be aware of.
We have not long passed February 2026 – the two-year anniversary of Biodiversity Net Gain (BNG) becoming mandatory for major developments in England.
Throughout the life of the Statutory Biodiversity Metric (SBM), there have been some minor changes in its operation.
In July 2025 there was the most significant array of changes made, including habitat feature definition updates, clarifications on strategic significance with published Local Nature Recovery Strategies (LNRS), watercourse riparian zone definitions, and more. These were notable, but we are now seeing upcoming changes that are of much greater significance.
Brownfield changes and others
In May 2025, a consultation was launched by the government on BNG and brownfield developments.
Brownfield sites have proven to be particularly awkward in their implementation of BNG. Within the urban landscape, what might look like an unappealing urban Site could in fact be of great local (and sometimes national) significance to biodiversity. This is the case with open mosaic habitats on previously developed land (OMH) – a humble but unique habitat. These can appear quite nondescript, and be as small as 0.25 ha (roughly a quarter of a football field). Any loss of this habitat in developments can be exceedingly difficult to compensate for. They are difficult to create and maintain, and are in short supply for anyone seeking them for off-site compensation. The consultation was rightly called for.
In April 2026, the government summarised the responses to this consultation and expounded the next steps forward.
Four main areas were discussed:
- Improving exemptions
- Streamlining the BNG metric process
- Increasing flexibility to go off-site for minor development
- Brownfield development with open mosaic habitat
Improving exemptions
Any development below 0.2 ha will be exempt from BNG. It is anticipated that this move will exempt around 50% of residential planning permissions that were previously required to undertake BNG. This would reduce the demand for off-site compensation by an estimated 10%. This change is expected to be implemented in July 2026.
While this wouldn’t effect OMH (as to qualify the habitat has to be greater than 0.25 ha), it will have an extremely significant impact upon the wider BNG scene.
Further exemptions are expected to be brought in within late 2026, including for developments where the primary objective is to conserve or enhance biodiversity, and for those that enhance parks, playing fields and public gardens.
Streamlining the BNG metric process
The SBM being an Excel document poses some problems, and it would be fair to say that it could be considered clunky. It was announced that there were plans to digitize the metric into an online accessible format. No timeline has been provided for this change.
The small sites metric (SSM) will be subject to a number of changes, including allowing its use for sites below 1 ha, adjusting trading rules to allow more effective onsite enhancement, simplifying habitats, and providing identification aid of habitats.
Watercourses are proving difficult to deal with for minor developments, and so changes are being considered such as simplifying the condition assessment and exploring a new distinctiveness category for heavily modified watercourses.
Increasing flexibility to go off-site for minor development
For minor developments, the biodiversity gain hierarchy will be amended to equalize the preference for on-site and off-site enhancements.
The only detriment in going off-site for compensation will be from the spatial risk category. This encourages off-site compensation to be found within the local area. The locality was previously defined as within the local planning authority boundary, but will now be defined as within the LNRS area the development occupies. LNRS areas average five LPAs each (excluding the London LNRS, which covers 32!), and so this change will allow developers to seek more widely for their off-site compensation without being penalized.
Brownfield development with open mosaic habitat
There is a significant gulf between OMH and the next highest value urban habitat within BNG. Even if a habitat falls just short of qualifying for OMH, the yield of habitat units drops enormously (within the SBM, OMH is worth 3x more units than the habitat on the rung below). With this, the government intend on exploring the option of introducing a new habitat between these that can be used to bridge this gap. They also intend on exploring the option of allowing for habitats that provide similar ecological value to OMH to be used for off-site compensation when OMH has been lost. OMH demands that it be replaced like-for-like, and so this change would make this rule less stringent.
BNG and Nationally Significant Infrastructure Projects (NSIPs)
At the same time as the brownfield consultation, there ran a parallel government consultation on BNG for NSIPs.
It was anticipated that NSIPs would be made subject to BNG in November of 2025, but this has been pushed back to November 2026.
April 2026 also brought us the parallel release of these NSIPs consultation responses.
A significant change is that the total biodiversity units required will no longer be calculated based upon the entire site, but only on those habitat areas that are to be impacted. Those other habitats not to be impacted can still be utilized for the gains, but will not serve to increase the required biodiversity units to hit 10% net gain.
Any loss of a habitat that is reinstated to its type and condition within 2 years of it being impacted is considered temporary loss. This timeframe will be increased to 5 years for NSIPs, as the government acknowledges that ‘NSIPs typically have longer timescales for temporary impacts than TCPA (Town and Country Planning Act) developments’.
A small but interesting note that also comes from this is that the 30-year securing of habitats is required, but there will also be the expectation that there should be basic maintenance of the habitats throughout the lifespan of the NSIP. This is not expected of other developments, and so works towards securing truly long-term biodiversity enhancements.
Similar to the changes for minor developments, NSIPs will be able to, in the first instance, pursue on-site or off-site for 10% net gain delivery. This will allow reasonable flexibility, especially for those longer linear projects.
Takeaway thoughts
BNG is set to prevent between 6,000 and 10,000 ha of habitat loss annually[1]. It is an extraordinary piece of legislation in its ability to enhance our country’s biodiversity. With its introduction to NSIPs, and the government’s actions intending to streamline the BNG process generally, we hope to see not just a moderation of biodiversity loss, but a renaissance of biodiversity action within England.
It is encouraging to see that concerns surrounding brownfield sites have been heard, and that action is being taken to refine the process and allow an easier, more comprehensive approach to achieving net gain for our biodiversity.
More detailed information published by Defra can be found on the gov.uk website. If this raises any questions or you would like our support with any BNG projects, feel free to get in touch with us.
