Biodiversity Net Gain (BNG) is a way of creating and improving natural habitats through the planning process. Biodiversity net gain is needed, as one of many actions, to address the significant and troubling losses in biodiversity and bio-abundance.
Under the Environment Act 2021, development must achieve at least a 10% net gain in biodiversity value, compared to the pre-development baseline, unless the development is exempt.
Exempt developments
Exempt developments include, for example, householder applications and developments of 0.2 hectares or below. For a full list of biodiversity net gain exempt developments please visit the GOV.UK website.
For any new planning application made or after 6 August 2026 the self-build and custom build exemption no longer applies.
Eligible developments
A standardised calculation tool is used, known as the biodiversity metric, to ensure consistency and transparency. This must be submitted with the planning application. The number of biodiversity units is based on the area of the habitat, its distinctiveness and its condition.
Under the biodiversity gain hierarchy, on-site gain i.e. within the red-line application site should be the first step (Please note that a post-development private garden is discounted because it has no public access and biodiversity net gains cannot be legally secured).
If this is not achievable then BNG can be delivered through a mixture of on-site and off-site. You can either make off-site biodiversity gains on your own land outside the development site or buy off-site biodiversity units on the market. Buying statutory credits from the government should be the last resort.
If you need to purchase off-site units, you may find the following unit finder websites of use (Please note that these websites have not been verified or endorsed by the Council and other sources may be available):
Future Homes Hub UK (external link)
Gaia - BNG Marketplace (external link)
Local Biodiversity Units Available - Habitat Bank Network (external link)
BNG Finder - Find and Sell Biodiversity Units (external link)
Whether you are relying on on-site or off-site habitat enhancements, you must achieve the 10% gain. A biodiversity gain plan to show how this will be achieved must be submitted after the approval of your planning application.
A Habitat Management and Monitoring Plan (HMMP) details how the creation, management and monitoring for a minimum statutory period of 30 years will be achieved. A HMMP is required when delivering ‘significant’ on-site gains, or for off-site land or units. A draft HMMP is required to be submitted with your planning application.
A HMMP will be secured by a s106 legal agreement (or conservation covenant). A legal agreement will secure a financial contribution to cover the 30-year monitoring fees. The contribution is based upon the habitat complexity and the size of your scheme. It is calculated to account for staff and resource expenditure, plus inflation and indexation. For more information on the cost specific to your development, please contact your appointed planning case officer.
For further information on what qualifies as a significant enhancement and for any other guidance and information please see the full collection of Biodiversity Net Gain webpages on the GOV.UK website (external link).
Council requirements
If your development is exempt, please ensure that you complete the necessary questions on the planning application form. Your planning application will be invalidated if these questions are not completed.
For eligible developments only, please ensure that you complete the Council’s Biodiversity Statement template, link below. Your planning application will be invalidated if this template is not completed and submitted.