Mandatory Biodiversity Net Gain – changes from 12 February 2024

Biodiversity net gain is a government strategy to ensure that habitat for wildlife is in a better state than it was before development. The habitat is in effect used as a proxy for calculating biodiversity.

The Government have hailed this to be a significant milestone in the delivery of their Environmental Improvement Plan, to ensure new development contributes to the recovery of nature and to meet the target to halt the decline in species abundance by 2030.

What is happening from 12 February 2024?

In England, a biodiversity plan will be mandatory for new planning applications for major development (includes residential developments with 10 or more dwellings, or where the site area is greater than 0.5 hectares) made under the Town and Country Planning Act 1990 (TCPA), subject to confirmed exemptions. Developers will be required to set out how the post-development biodiversity value must improve by at least 10% of the biodiversity value on the site prior to development. This increase in biodiversity value is “the Biodiversity Net Gain”. These changes have been introduced by virtue of the Environment Act 2021 (Commencement No 8 and Transitional Provisions) Regulations 2024 (Sl 2024/4).


  1. ‘Small sites’ (includes residential development where the number of dwellings is between 1 and 9, or where the site area is less than 0.5 hectares) for which the mandatory requirement will not be introduced until 2 April 2024 by virtue of the Biodiversity Gain Requirements (Exemptions) Regulations 2024 (SI 2024/47).
  • It is believed that this approach is intended to lessen the burden on local authorities.
  1. Nationally Significant Infrastructure Projects for which the mandatory requirement will not apply until late November 2025.
  2. Planning applications which are not made under the TCPA – Regulations will be needed to make BNG apply to these.
  3. Developments which do not impact an onsite priority habitat (as set out in a list published under section 41 of the Natural Environment and Rural Communities Act 2006) where the impact of the development will be minimal.
  4. Householder applications.
  5. Planning permissions in relation to high speed railway transport networks.
  6. Biodiversity gain sites.
  7. Self-build and custom build applications.

How will this affect you as a developer or landowner?

(a) Developers

Biodiversity net gain is intended to make developments more attractive for potential residents and the local community. Those developers who provide more than 10% of biodiversity net gain can allocate the excess to other development to help offset the cost of their own development.

Developers are encouraged to hire a competent person (e.g., an ecologist) to use the statutory biodiversity metric. They must attach a metric tool calculation, showing the site’s biodiversity value before development to the planning application. Information as to how the biodiversity net gain requirement will be met will also need to be provided. The Local Planning Authority must approve the biodiversity gain plan before development begins. The link below refers to the Government guidance on the steps regarding how to meet biodiversity net gain requirements: Meet biodiversity net gain requirements: steps for developers – GOV.UK (

(b) Landowners

Landowners have been provided with another way to fund nature recovery, alongside providing an alternative income stream to complement other business activities. Landowners can provide land for off-site Biodiversity Net Gain improvements and be paid by developers to maintain this in an improved condition to assist developers to meet this obligation, provided that the habitat sites are registered. However, landowners must cautiously note that the obligations they would enter into would last for the required minimum of 30 years. Please refer to the below link to review the Government guidance on the steps regarding how to meet biodiversity net gain requirements: Meet your BNG requirements: steps to take for land managers – GOV.UK (


All parties must be aware and understand how the new requirements will affect them. This topic is likely to be raised during conversations with planning consultants and within option agreements and conditional contracts. Our Development team at Herrington Carmichael LLP are dedicated to Biodiversity Net Gain and regularly act for developers and landowners. If you would like to discuss your requirements, please contact us to speak to a member of our Real Estate Team.

Jessica de Noronha
Senior Solicitor, Real Estate
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This reflects the law and market position at the date of publication and is written as a general guide. It does not contain definitive legal advice, which should be sought in relation to a specific matter.

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