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Biodiversity Net Gain for new development

After a prolonged and delayed legislative gestation period new developments in England will now have to provide a 10% net gain in biodiversity. This requirement applies to planning applications submitted for major development (i.e. for 10 or more homes or more than 1,000sqm of non-residential floorspace) after 12th February 2024 and from 2nd April 2024 for most minor forms of development.

While there has already been a requirement for some time in national and some local plan policies for biodiversity net gain (BNG) the legislation introduces a non-negotiable requirement to provide a minimum of 10% gain.  The requirement is achieved through a statutory planning condition that for all relevant developments, the development may not begin unless a biodiversity gain plan has been submitted to the planning authority and the planning authority has approved it.

The Baseline Value

Details of the pre-application baseline value of a site must be assessed and submitted with all relevant planning applications, failing which the local planning authority will refuse to validate the application. For BNG, biodiversity is measured in standardised biodiversity units. The baseline value is assessed using what is known as the official biodiversity metric.  This is a way of measuring biodiversity value for the purposes of BNG. It measures all types of habitats, including grassland, hedgerows, lakes, woodland, and watercourses. Developers will have to get a competent person such as an ecologist to use the metric tool and advise.

The biodiversity baseline date will generally be the date before the application is submitted, however if a habitat has been deliberately degraded since 30th January 2020, the local planning authority can insist that the baseline is taken as the pre-clearance biodiversity value.

The BNG requirement for developments

To satisfy the statutory BNG condition the developer must show that 10% BNG can be achieved. This is also calculated using the biodiversity metric and involves the submission and approval of a biodiversity gain plan.

There are three ways that 10% BNG can be achieved:

1. On-site: Through enhancing and restoring biodiversity within the planning application boundary (not within other land owned by the developer, which is regarded as ‘off-site’). 

2. Off-site: If a developer cannot achieve on-site BNG, or can only partly achieve it, they can enhance/restore habitats on other land (off-site). This might be land they own, or they can buy off-site biodiversity units on the market from ‘BNG land banks’. Technically off-site BNG can be provided anywhere in England, however the BNG Metric contains a ‘spatial risk multiplier’ for off-site mitigation, which reflects the distance of habitat changes from the development site. The further away the offset is from the development site, the more biodiversity units the developer will have to buy.  This is to ensure as far as possible that BNG enhancements directly benefit the area where the development is taking place.

3. Biodiversity Credits: As a last resort a developer must buy statutory biodiversity credits from the government, which will use the revenue to invest in habitat creation.

The biodiversity gain plan cannot be submitted before planning permission is granted, although a draft can be supplied for discussion as part of a planning application.

‘Significant’ on-site biodiversity gains, and all off-site biodiversity gains, will be controlled either by Section 106 agreements, or conservation covenants. A conservation covenant is a private legal agreement, made in writing, between a responsible body and a landowner, which establishes that land will be used for a conservation purpose.  Responsible bodies are approved by Defra and can be a local authority, a public body or charity, where at least some of its main purposes or functions relate to conservation or a private sector organisation, where at least some of its main activities relate to conservation. This does mean that we are going to see an increasing need for legal agreements following the grant of planning permission to secure the delivery of BNG before developments can start.

Exempt Development 

There are a number of exemptions from the BNG requirements, including:

  • Section 73 and 96A applications – Section 73, where the original planning permission was exempt because it was submitted before 10% BNG became mandatory; retrospective applications where development was carried out before the date of the application (section 73A). Amendments to a planning permission which are considered to be ‘non-material’ (section 96A).
  • Householder applications – extension/development on existing dwellinghouses.
  • Self-build and custom build applications – developments of no more than 9 dwellings; carried out on a site which has an area no larger than 0.5 hectares; and consists exclusively of dwellings which are self-build or custom-build.
  • Permitted Development - under the General Permitted Development Order (GPDO).
  • ‘De minimis’ applications


If you have any questions or would like any further information on these issues, please contact John Bosworth or Robin Barnes.


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