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Biodiversity net gain (BNG): government blog posts clarify statutory metric and exemptions

Reasons to choose Wilson Browne

On 22 and 24 January 2024, the Department for Environment, Food and Rural Affairs (Defra) published two blog posts on mandatory biodiversity net gain (BNG), on exemptions and on the statutory biodiversity metric. BNG commences for new development in England on 12 February 2024. The requirement for developers will be to provide BNG of at least 10% for new planning applications for development under the Town and Country Planning Act 1990 that results in loss or degradation of habitat.

The blog post on exemptions from the BNG requirement confirms that the list is narrow and focused on five categories:

  • development below a de minimis threshold
  • development of an existing house
  • off-site biodiversity gain sites that require planning permission
  • small-scale self-build and custom house building of no more than nine dwellings and up to 0.5 hectares
  • the High Speed Railway Transport Network.

The de minimis threshold is development that does not impact a priority habitat and impacts less than 25 square metres of non-priority onsite habitat (such as modified grassland) or five metres for non-priority onsite linear habitats (such as native hedgerows).

Development of an existing house does not include change of use or number of dwellings. The self-build exemption applies whether it is a standalone development site or secured as part of a major development.

The blog post on the metric confirms that Defra has laid it before Parliament and the statutory biodiversity metric calculation tool has been published. Developers must use the metric to demonstrate BNG and land managers must also use it when supplying off-site units to such developments. The metric uses habitats as a proxy for biodiversity and calculates biodiversity value in standardised biodiversity units.

Ika Částka


Ika Částka

Senior Partner

Ika is Head of the Commercial Property team and has been advising individuals and businesses across Northamptonshire since 1986, specialising in commercial, agricultural and rural property matters for both businesses and individuals.