Biodiversity Net Gain (BNG) introduced through the Environment Act 2021, requires most developers to deliver at least 10% increase in biodiversity and to secure those obligations for a minimum of 30 years. These obligations are usually secured through planning conditions or Section 106 Agreements.

BNG became mandatory for certain developments in 2024 and since that time has continued to attract criticism from the development sector, with concerns around uncertainty, cost pressures and delays prompting renewed calls for reform.

In May 2025, the Government launched a consultation regarding the improvement of the implementation of BNG for minor, medium and brownfield development (“the Consultation”). On 15 April 2026, the Government published its response signalling a shift towards significant reforms to be made to the current BNG exemptions.

The blog outlines the key proposed changes, which can be summarised as follows:

A new area-based exemption to apply to all development types where the site area within the red line boundary is 0.2 hectares or less
Removing the exemption for small scale self-build and custom build development
The retention of the de minimis exemption subject to the brownfield consultation
New exemptions will be introduced with the intention to be implemented before 31 July 2026

A new area-based exemption

The Government has confirmed that a new area based exemption will apply to all developments where the site area within the red line boundary is 0.2 hectares or less. This is not an extension of the existing de minimis exemption but rather a new category of exemptions all together.

The stated aim of this exemption is to simplify the planning process, reduce the impact of BNG on development and improve biodiversity. The Government estimates that this exemption will affect around 50% of residential planning permissions that would ordinarily have been required to comply with BNG regulations. It is important to note that developments which are exempt from BNG requirements will nevertheless remain subject to environmental protections through planning policy and guidance and wider regulatory requirements.

The existing rules to irreplaceable habitats remain unchanged and it has been reaffirmed that BNG does not apply in these circumstances. They have further confirmed that this exemption will not apply where onsite priority habitats are impacted.

Removal of self-build and custom-build exemption

At present, self-build and custom-build developments are exempt from BNG. The Government intends to remove this exemption noting that most small scale single dwellings will be covered by the new 0.2 hectare area based exemption.

As outlined in the Consultation response, the change is expected to reduce administrative burdens for local authorities and simplify the BNG framework for developers.

‘De-minimis’ exemption

The de-minimis exemption is designed to ensure that developments which have very limited impact on BNG are not subject to disproportionate BNG requirements.

Further changes to the de minimis exemption will be considered alongside the Government’s response to the consultation on BNG for residential brownfield development. However, the Government has indicated that some exemptions are likely to remain necessary to cover particular forms of development such as:

Change of use applications
Installation of solar panels on an industrial building
Replacement of a petrol station with an electric vehicle charging station
An upward extension of a large block of flats

The brownfield development consultation

As for the brownfield consultation itself, the Government is considering an exemption for “brownfield residential development” on a range of different area based thresholds and the proposals are between 0.5 and 2.5 hectares. The proposed definition for “brownfield development” mirrors the approach used in the Building Safety Levy regulations, requiring at least 75% of the site to be previously developed land.

New exemptions

The Government intends to introduce new exemptions by regulation for:

Development whose primary objective is to conserve or enhance biodiversity
Temporary planning permissions covering permissions granted for a maximum of 5 years
Development enhancing parks, playing fields and public gardens

Timelines

The changes arising from the Consultation and the subsequent response will be implemented in several stages, though secondary legislation and updated guidance.

The aim is that the first set of changes will come into force by 31 July 2026. These regulations will be:

Introduce the new 0.2 hectare are based exemption
Remove the self and custom build exemption
Exempt temporary planning permissions granted for a maximum of 5 years
Amend the biodiversity gain hierarchy for minor development only

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

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

Depending on the outcome of the consultation on a possible BNG exemption for brownfield residential development, the secondary legislation could also include:

Changes to the de minimis threshold
The introduction of a new, targeted exemption for residential brownfield development if taken forward following consultation

Until the proposed changes take effect, the current BNG requirements remain fully in force.

Whilst this does not go as far as many in the development and housebuilding sectors would like to see, there is some movement to adapting BNG requirements to commercial reality, and in some cases addressing stark unfairness, for instance the current imposition of BNG on the vast majority of “temporary” or time limited planning permissions.

Get In Touch

If you would like any advice regarding compliance with BNG requirements, the Planning Team at Lester Aldridge would be happy to assist. Please do get in touch to speak with a member of the team.