28 October 2026
The Government’s 2026 Budget has announced further changes to Biodiversity Net Gain (BNG), including a new exemption for residential developments on brownfield sites of up to 1.5 hectares in England.
The announcement follows a series of changes introduced earlier this year, which have already reduced BNG requirements for smaller developments. Taken together, these reforms represent a significant shift in how BNG is being applied through the planning system.
While the Government argues that the changes will reduce costs and delays for developers, they have also raised questions about the potential implications for biodiversity, particularly on previously developed land that can support valuable habitats.
What Has Changed?
The main announcement in the 2026 Budget is that residential developments on brownfield sites of up to 1.5 hectares will be exempt from mandatory BNG requirements.
The Government hopes that removing this requirement will make smaller brownfield housing developments more financially viable and help deliver its wider housebuilding objectives.
However, the exemption is not yet in force. Further details, including the implementation date and precise eligibility criteria, are expected to be published alongside the Government’s response to its earlier consultation.
Until the new exemption comes into effect, developers will need to comply with the existing BNG requirements.
Further Changes Introduced Earlier in 2026
The Budget announcement follows several important amendments to the BNG regulations that came into effect on 6 August 2026.
Perhaps the most significant was the introduction of an exemption for developments on sites measuring 0.2 hectares or less, provided that no onsite priority habitat is affected.
This means that many small developments no longer need to demonstrate the statutory 10% biodiversity net gain previously required under the Environment Act 2021.
Other changes included:
- Temporary developments: An exemption for developments permitted for five years or less, provided that onsite priority habitats are not affected.
- Greater flexibility for minor developments: Smaller developments that remain subject to BNG can now consider offsite biodiversity gains without first having to prioritise onsite habitat creation or enhancement.
- Self-build and custom-build developments: The previous specific exemption has been removed for new applications, although some projects may qualify under the new 0.2-hectare exemption.
These changes generally apply to planning applications submitted on or after 6 August 2026, with transitional provisions for earlier applications and permissions.
What About Larger Developments?
While the Government is reducing BNG requirements for smaller sites, the requirements are being extended to major infrastructure projects.
From 2 November 2026, mandatory BNG applies to new applications for Nationally Significant Infrastructure Projects (NSIPs) in England, subject to the relevant statutory provisions.
This brings major infrastructure developments, including certain energy, transport and water projects, within the BNG framework.
The approach appears to reflect a Government preference for concentrating mandatory biodiversity gains on larger developments while reducing the regulatory burden on smaller schemes.
Could the Changes Affect Valuable Brownfield Habitats?
One concern with the proposed brownfield exemption is that previously developed land is not necessarily of low ecological value.
Some brownfield sites support species-rich grassland, scrub and open mosaic habitats that have developed naturally over many years. These habitats can provide important opportunities for invertebrates, reptiles, birds and other wildlife, particularly in urban areas where suitable habitat is increasingly fragmented.
The ecological value of such sites is not always immediately apparent. Areas that appear untidy, overgrown or derelict can sometimes support greater biodiversity than more intensively managed green spaces.
Exempting qualifying brownfield developments from BNG could therefore remove an important mechanism for securing habitat creation and enhancement.
It remains to be seen how the final exemption will address sites containing priority habitats and other features of ecological importance.
Does a BNG Exemption Mean Ecological Surveys Are No Longer Required?
No. This is an important distinction.
An exemption from mandatory BNG does not remove the need to consider biodiversity through the planning process.
Developers may still need to commission a Preliminary Ecological Appraisal (PEA) and, where appropriate, undertake further protected species surveys to identify potential ecological constraints.
Existing requirements relating to protected species, designated sites, important habitats and ecological mitigation will continue to apply.
Local planning policies may also require biodiversity protection or enhancement, even where a development is exempt from the statutory 10% BNG requirement.
For this reason, ecological considerations should still be addressed at an early stage in the design and planning process.
What Do the Changes Mean for Developers?
For developers, particularly those bringing forward smaller residential schemes, the changes are likely to be welcome.
Removing the requirement to calculate and deliver 10% BNG on qualifying sites could reduce ecological assessment costs, avoid the need to purchase offsite biodiversity units and simplify the planning process.
However, determining whether a development qualifies for an exemption will be important.
The size of the application site, the presence of priority habitats, the type of development and the date of the planning application can all influence whether BNG is required.
Developers should therefore seek ecological advice before assuming that a project is exempt.
Our View
BNG has provided an important mechanism for ensuring that development makes a measurable contribution towards nature recovery. However, applying the same requirements to developments of very different sizes and ecological impacts has presented practical challenges.
The introduction of a 0.2-hectare exemption is a sensible attempt to make the system more proportionate, particularly where small developments affect habitats of limited ecological value.
The proposed exemption for residential brownfield sites of up to 1.5 hectares is potentially more significant.
Many brownfield sites have relatively low biodiversity value, and the costs associated with meeting BNG requirements can sometimes be disproportionate. However, others support habitats of considerable ecological importance.
A blanket exemption based primarily on site size and previous land use risks overlooking this distinction.
Ultimately, the success of these reforms will depend on whether they reduce unnecessary costs and delays without weakening the protection of habitats that genuinely matter for biodiversity.
What Happens Next?
Further details of the brownfield exemption are expected following publication of the Government’s consultation response and associated impact assessment.
Additional changes to the statutory biodiversity metric are also anticipated, including revisions intended to address some of the challenges associated with assessing brownfield habitats.
For now, developers and planning professionals should continue to apply the existing BNG regulations while keeping track of the forthcoming changes.
If you are planning a development and are unsure how the latest Biodiversity Net Gain changes might affect your project, get in touch with Acer Ecology. Our experienced team can advise on BNG requirements, ecological surveys and potential constraints, helping you navigate the planning process and avoid unnecessary delays.
For further information or a quotation, email enquiries@acerecology.co.uk or call 029 2065 0331. Alternatively, visit our contact page.
