biodiversity net gain

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In Plain English: Biodiversity net gain

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Updated June 2025

Biodiversity net gain (BNG) was introduced by the Environment Act 2021. It is an approach to planning and development that aims to ensure development leaves the natural environment in a measurably better state than it was before.

BNG requirements should enhance and create natural habitats and help towards building the resilience of wildlife and its ability to adapt to climate change.

Since 12 February 2024, it has been mandatory for most Town and Country Planning Act developments granted planning permission to provide a minimum 10% net gain in biodiversity, measured against pre-development figures. This was extended to ‘small sites’ from 2 April 2024. There are a few exemptions for very small sites, homeowner applications and custom/self-build applications. It is expected that BNG will be mandatory for Nationally Significant Infrastructure Projects (NSIPs) from November 2025.

Local planning authorities can set local plans to seek additional biodiversity net gains above the national minimum of 10%, as long as there is evidence to demonstrate that this does not affect the viability of the delivery of the Local Plan. Currently there are a few examples of LPAs either proposing (or having adopted) a 20% uplift in biodiversity – examples include Guildford Borough Council and Worthing Borough Council.

Biodiversity uplift can be achieved through habitat creation or enhancement on-site and/or off-site, or through the purchase of statutory biodiversity credits from the government. The mitigation hierarchy for BNG is set out in national policy. Developers are encouraged to follow these steps in order to:

  1. Avoid or reduce biodiversity impacts through site selection and development layout;
  2. Enhance and restore biodiversity on-site;
  3. Create or enhance off-site habitats, either on the developer's own land or by purchasing biodiversity units
  4. As a last resort, purchase statutory biodiversity credits from the UK government (if they can demonstrate that they are unable to achieve biodiversity net gain through on-site or off-site measures).

BNG units are legally secured either through a Section 106 agreement or Conservation Covenant, and managed for a minimum of 30 years either on or off-site. Where credits are bought from the government, the council would disclose a mandatory BNG contribution fee (per biodiversity unit) upon issuing planning permission, which would fund net gain provision elsewhere. While local authorities will be able to sell biodiversity units, developers can also negotiate to purchase credits from local landowners or other developers with an excess of biodiversity units.

Initial estimates from Department for Environmental, Food and Rural Affairs (Defra) placed biodiversity units at anywhere between £9,000 and £15,000 per unit, though the emerging market has unit prices starting at approximately £25,000 for grassland units up to £125,000 for watercourse units.

Current guidance states that all relevant planning applications will need to be accompanied by biodiversity net gain information, including:

  • The pre-development ‘baseline’ value measured using the most recent Defra biodiversity metric;
  • The proposed approach to enhancing biodiversity on-site:
  • Any proposed off-site biodiversity enhancements that have been planned or arranged.

The BNG requirement will be framed as a pre-commencement planning condition, meaning that the Biodiversity Gain Plan must be approved by the local planning authority, allowing for the condition to be discharged before development can begin.

Following the Natural England consultations there is now further guidance and standard templates of the documents required for delivering BNG, including template Management Plans for on/off-site delivery of habitat.

 

Further information

Contact Johnny Campbell or Jon Dearsley

New rules for biodiversity: what landowners and developers need to know

 

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