Government confirms forthcoming changes to Biodiversity Net Gain rules

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The UK Government has published its response to a consultation on improving the implementation of Biodiversity Net Gain (BNG) for minor, medium and brownfield development, setting out a package of reforms expected to come into force before 31 July 2026 (subject to parliamentary scheduling).

BNG remains “widely considered to be a world-leading environmental policy”, and Government has reiterated that it “remains committed to BNG and recognises the importance of BNG in delivering nature-positive homes and infrastructure that this country needs.”

However, the response is primarily aimed at reducing burdens on developers (especially smaller ones) rather than strengthening outcomes for nature.

Key changes confirmed

Central to the reforms is the introduction of a new area-based exemption for sites of 0.2 hectares or below (except where priority habitats are present). Government expects this to exempt around 50% of residential planning permissions from BNG requirements.

This change is estimated to result in:

  • around 12% fewer baseline biodiversity units being compensated for; and
  • a reduction of around 10% in demand for off-site biodiversity units.

While Government considers these changes “proportionate” and argues that they will focus effort on larger developments with greater potential to deliver environmental benefits, the cumulative effect is likely to reduce overall gains for nature recovery.

Alongside this, regulations will:

  • remove the self-build and custom build exemption (widely seen as abused and unworkable in practice);
  • introduce a new exemption for temporary developments of up to five years;
  • amend the biodiversity gain hierarchy for minor development; and
  • introduce new exemptions for developments primarily focused on conserving or enhancing biodiversity.

Legislative roadmap and implementation

Defra has set out a clear legislative pathway for implementing these reforms.

Before summer recess 2026, secondary legislation will be brought forward with the intention of changes coming into force before 31 July 2026 (as noted above, subject to parliamentary scheduling). These regulations will:

  • introduce the new 0.2 hectare area-based exemption;
  • remove the self and custom build exemption;
  • exempt temporary planning permissions granted for a maximum of five years; and
  • amend the biodiversity gain hierarchy for minor development only.

Later in 2026, following the Government’s response to the consultation on a potential additional exemption for residential brownfield development, further secondary legislation is expected to:

  • exempt development whose primary objective is to conserve or enhance biodiversity; and
  • exempt targeted development that enhances parks, playing fields and public gardens.

Depending on the outcome of the brownfield consultation, this later legislation could also include:

  • changes to the de minimis threshold; and
  • the introduction of a new, targeted exemption for residential brownfield development.

To support implementation, Defra and the MHCLG will review and update guidance, planning application forms and biodiversity gain plan templates. Guidance on transitional arrangements will also be issued, clarifying how applications should be treated while changes are being phased in.

The Government will continue to fund the Planning Advisory Service to provide training and targeted support to local planning authorities.

Until the new regulations take effect, the current BNG requirements remain in place. Developments granted permission subject to the biodiversity gain condition must still submit and secure approval of a biodiversity gain plan before development can commence.

Changes to the biodiversity metric

The Government has also confirmed a programme of updates to the statutory biodiversity metric, which will require the relevant statutory instrument to be re-laid before Parliament.

Proposed changes include:

  • reform of the spatial risk multiplier;
  • updates to metric definitions, condition assessments and guidance for open mosaic habitats (OMH);
  • potential creation of a new medium distinctiveness urban habitat category;
  • allowing alternative habitat delivery as compensation for loss of OMH;
  • potential changes to watercourse condition assessments; and
  • consideration of a new distinctiveness category for heavily modified watercourses.

Updated metric tools and user guidance are expected later in 2026, again subject to parliamentary scheduling. Further technical work is required on watercourse elements, which may be progressed separately if needed.

Transitional arrangements will be provided for projects already using the current metric.

In parallel to the above, Defra intends to move toward a more accessible, integrated digital metric service, although in the short term updates may continue to be delivered through existing Excel tools.

Ongoing issues with exemptions

The consultation response acknowledges that the current system can be complex and, in some cases, disproportionately costly. However, the growing number of exemptions risks making the system harder to navigate while also diluting its environmental impact.

There is broad agreement across the sector that the current de minimis exemption has been open to misuse. It is positive that Government has committed to reviewing this loophole, although the decision has been delayed pending further consultation on brownfield development.

Supporting delivery and looking ahead

The Government highlights that there are already “excellent examples from both the public and private sector of BNG delivery”, supported by best practice guidance, training and a growing ecosystem of tools.

It also recognises that developers, habitat providers and ecologists “need stability”, and that this response is intended to provide clarity on forthcoming changes.

Overall, while the reforms respond to genuine delivery challenges the cumulative impact of exemptions is likely to reduce the total contribution BNG makes to nature recovery.

For BNG to succeed at scale, what is now needed is a stable, consistent framework that gives confidence to practitioners, investors and local authorities alike and at the same time maintains ambition for biodiversity outcomes and nature recovery.