Biodiversity Net Gain
New Exemptions and Rules from August 2026
The Biodiversity Net Gain (BNG) regime has undergone a significant change, with new exemptions and greater flexibility for smaller developments taking effect from 6 August 2026.
The reforms are intended to reduce the cost and administrative burden associated with BNG for smaller development sites, while retaining the existing requirements for larger developments and protecting important habitats.
For developers and landowners, the changes may mean that some projects previously subject to mandatory BNG are now exempt, while others will have greater flexibility over how the required biodiversity gain is delivered. However, the date on which a planning application is submitted will be important, and exemption from BNG does not remove wider ecological and planning obligations.
The background and original BNG regime
Mandatory Biodiversity Net Gain was introduced in England in February 2024 under the Environment Act 2021 and the Town and Country Planning Act 1990 planning regime.
Unless an exemption applies, development subject to BNG must deliver at least a 10% increase in biodiversity value compared with the site’s pre-development position. The biodiversity gain must generally be secured for at least 30 years.
Applicants are required to use the statutory biodiversity metric to calculate biodiversity value and submit a biodiversity gain plan before development can commence.
The original regime also incorporated a biodiversity gain hierarchy. Developers were generally expected to avoid the loss of important habitat and prioritise the creation and enhancement of habitat on the development site before looking to off-site biodiversity gains.
However, concerns subsequently emerged about the practical operation of BNG, particularly for smaller sites. In 2025, the Government consulted on reforms intended to simplify the regime for minor, medium-sized and brownfield development, including possible changes to exemptions, the biodiversity metric and the ability to use off-site biodiversity gains.
What is changing?
Following the consultation, a number of important changes took effect on 6 August 2026.
Sites of 0.2 hectares or less
Perhaps the most significant is a new exemption for developments on sites of 0.2 hectares or less. Qualifying developments will no longer have to deliver mandatory BNG, provided they do not negatively affect an on-site priority habitat.
Temporary developments
A separate exemption has also been introduced for certain temporary developments where the land will be reinstated within five years or less. Again, this exemption is subject to the protection of priority habitat.
Previous temporary periods relating to the same development are taken into account when considering the five-year period.
Minor developments
The rules surrounding the biodiversity gain hierarchy have also been relaxed for minor developments. Previously, applicants were generally required to prioritise on-site biodiversity enhancement before looking off-site. From 6 August, this requirement applies only to major development. Qualifying non-major schemes that remain subject to BNG can therefore use off-site biodiversity units without first having to demonstrate that sufficient on-site enhancement cannot be achieved.
Removal of exemption for self-build and custom-build development
There is, however, one change that potentially brings more development within the BNG regime: the existing exemption for self-build and custom-build development has been removed. Such developments must now comply with mandatory BNG unless another exemption applies.
Who do the changes apply to?
The changes are particularly relevant to developers and landowners bringing forward small and non-major developments.
For the purposes of the biodiversity gain hierarchy, major development includes residential schemes involving 10 or more dwellings or sites of 0.5 hectares or more where the number of dwellings is not known. It also includes certain non-residential developments involving 1,000 square metres or more of floorspace or sites of one hectare or more, together with mineral and waste development.
Qualifying criteria for the new small-site exemption
From 6 August 2026, a development will generally fall within the new small-site exemption where:
- the development is non-major;
- the site is 0.2 hectares or less; and
- the development will not negatively affect priority habitat on the site.
A small residential infill development on previously developed land, for example, may therefore fall outside mandatory BNG altogether if these requirements are satisfied.
The existing de minimis exemption has not disappeared. It continues to be available for developments on sites larger than 0.2 hectares where its separate requirements are satisfied.
Developers should therefore consider all potentially applicable exemptions rather than assuming that a site exceeding 0.2 hectares must automatically deliver BNG.
What is a priority habitat?
Priority habitat is an important part of determining whether either of the new exemptions is available.
Priority habitats are habitats identified as being of principal importance for conserving or enhancing biodiversity under section 41 of the Natural Environment and Rural Communities Act 2006. Natural England’s Priority Habitat Inventory can assist in identifying whether priority habitat falls within the red-line boundary of a proposed development, while Local Environmental Records Centres may hold additional local habitat information.
Developers hoping to rely on an exemption should therefore establish at an early stage whether priority habitat is present and whether the proposed development would adversely affect it.
Greater flexibility
Not every smaller development will qualify for an exemption. However, the reforms may still make compliance easier where BNG continues to apply.
For non-major developments, the biodiversity gain hierarchy no longer requires applicants to demonstrate that on-site biodiversity opportunities have first been maximised. Instead, developers may choose to secure the necessary biodiversity gains off-site in the first instance.
This could be particularly useful for tightly constrained urban or brownfield sites, where providing habitat on-site may conflict with design, density or viability considerations.
Transitional arrangements
Timing will be important. The new regime applies to planning applications submitted on or after 6 August 2026. Applications submitted before that date will continue to be dealt with under the previous BNG rules.
Special transitional provisions also apply to applications made under section 73 of the Town and Country Planning Act 1990 to vary or remove planning conditions. The previous regime may continue to apply where the original application was submitted, or the relevant permission granted, before 6 August 2026.
Developers with existing or forthcoming applications should therefore establish which version of the regime applies before assessing their BNG obligations.
BNG exemption does not mean ecology exemption
Importantly, exemption from mandatory BNG does not remove the wider environmental obligations associated with development.
Protected species legislation, statutory site protections, planning policy and other ecological considerations continue to apply. Local planning authorities will also continue to consider biodiversity impacts through the planning process and the mitigation hierarchy.
Where significant ecological harm cannot be avoided, adequately mitigated or, as a last resort, compensated for, planning permission may still be refused.
Developers should therefore continue to consider ecology at an early stage even where they believe their project qualifies for a BNG exemption.
Future changes expected
The August reforms are not intended to be the final changes to the BNG regime. Further proposals include exemptions for development whose primary purpose is conserving or enhancing biodiversity and targeted exemptions for certain improvements to parks, playing fields and public gardens. Changes to the statutory biodiversity metric are also expected, while the Government has been considering a possible targeted exemption for certain residential brownfield development.
Comment
The August 2026 reforms represent a significant relaxation of the BNG regime for some smaller developments and should reduce both cost and complexity for developers who qualify for the new exemptions.
The changes to the biodiversity gain hierarchy may be equally important. Giving non-major developments greater freedom to use off-site biodiversity gains could make BNG considerably easier to accommodate on constrained sites.
However, the new rules do not amount to a general relaxation of environmental planning requirements. The protection afforded to priority habitats remains particularly important, while other ecological legislation and planning policies continue to apply regardless of whether mandatory BNG is required.
There may also be wider consequences. Environmental organisations have raised concerns that reducing on-site biodiversity requirements could mean fewer opportunities for habitat creation within developed areas, while the longer-term impact of the reforms on the market for biodiversity units remains uncertain.
With further reforms expected, developers and landowners should consider BNG requirements at the outset of a project, establish which regulatory regime applies and avoid assuming that a new exemption removes the need for wider ecological assessment and planning advice.
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