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Biodiversity net gain

Biodiversity net gain (BNG) is an approach to development. It makes sure habitats for wildlife are left in a better state than they were before the development, in a way that can be measured.

By law, developers must:

  • measure biodiversity when planning a development
  • make sure there is a BNG of at least 10% once the development is complete
  • make sure habitat management and monitoring is secured for at least 30 years

Unless covered within GOV.UK: BNG exempt developments, BNG requirements are mandatory for new planning applications:

  • from 12 February 2024 for major developments – this includes residential developments with 10 or more dwellings, or where the site area is more than 0.5 hectares
  • from 2 April 2024 for 'small sites'

Measuring biodiversity

The biodiversity value of a site is calculated using the 'statutory biodiversity metric tool' – for full details, go to GOV.UK: Statutory biodiversity metric tools and guides. This metric must be completed by an ecologist. They will assess the biodiversity value of the existing habitat and give advice on how suitable habitat can be created or enhanced for the land.

All areas must be measured and included in the metric, including woods, meadows, bare ground, arable farmland, hardstanding, lawns, flowerbeds, and so on. The metric calculates the number of 'units' on site based on factors such as the size, condition and habitat type.

Once the current number of units on site is known, the development must be planned to increase in this number by at least 10%.

The metric calculates what will be lost through a development. The net gain can be achieved on-site by improving existing habitat or creating new habitat. If it is not possible to provide all or part of the net gain on-site, then it must be provided off-site.

National guidance

For national guidance, go to:

The Natural England: Green Infrastructure Planning and Design Guide gives practical guidance on how to plan and design good green infrastructure, including how BNG can support the design.

Local guidance

Thurrock is part of the Essex Local Nature Partnership, which is responsible for the Essex Local Nature Recovery Strategy. The partnership promotes the co-ordination of BNG across the Essex local authority areas it represents. Go to Essex Design Guide: Biodiversity net gain.

Our Local Plan Initial Proposals suggest setting a BNG target of 20% in our new Local Plan. Policy directions and sites within the emerging Local Plan are still subject to change and do not currently have any meaningful weight when assessing planning applications.

By law, you must not include 'Irreplaceable Habitats' in your BNG process. 'Irreplaceable Habitats' in Thurrock currently include:

  • ancient woodland
  • Spartina saltmarsh swards
  • Mediterranean saltmarsh scrub