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Biodiversity Net Gain

The government has introduced Biodiversity Net Gain (BNG) as a way of creating and improving natural habitats. BNG makes sure development has a measurably positive impact or ‘net gain’ on biodiversity. This is compared to what was there before development.

In the Maidstone borough, residential developers are required to deliver on-site BNG of 20%. This means a development will result in more or better quality natural habitat than there was before development.

BNG is now mandatory for major developments from 12 February 2024. It will also become mandatory for small developments from 2 April 2024.

The Biodiversity Gain hierarchy

As stated in the National Planning Policy Guidance, the Biodiversity Gain Hierarchy and its effect for the purpose of the statutory framework for BNG is set out in Articles 37A and 37D of the Town and Country Planning (Development Management Procedure) (England) Order 2015.

This hierarchy, which does not apply to irreplaceable habitats, sets out a list of priority actions:

  • first in relation to onsite habitats which have a medium, high and very high distinctiveness (a score of four or more according to the statutory biodiversity metric), the avoidance of adverse effects from the development and, if they cannot be avoided, the mitigation of those effects and;
  • then, in relation to all onsite habitats which are adversely affected by the development, the adverse effect should be compensated by prioritising in order, where possible, the enhancement of existing onsite habitats, creation of new onsite habitats, allocation of registered offsite gains and finally the purchase of biodiversity credits.


Householder applications are exempt from BNG. You can check the list of exemptions to find out if your development is exempt.

If your scheme is self-build or custom build you will need to complete our proforma.

Statutory and local requirements

In the Maidstone borough, developers are required to deliver on-site BNG of 20%. This is made up of a 10% statutory net gain and a 10% local net gain.

Statutory 10% BNG

10% statutory BNG is a requirement under the Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021).

Additional local 10% BNG

The local BNG requirement is an additional 10%. It is required for residential development under the MBC Local Plan Review.

Amended Policy LPRSP14(A) requirement: "deliver a minimum 20% Biodiversity Net Gain on new residential development, having regard to Biodiversity Opportunity Areas and/or Nature Recovery Networks. Biodiversity Net Gain should be calculated in accordance with the latest Natural England/DEFRA biodiversity metric or equivalent".


You will need to consider BNG at each stage of your planning application.


You can apply for pre-application advice from the planning service.

You can also find out more about Biodiversity Net Gain in Kent before you apply.

Submitting a planning application

In accordance with the government guidance, when applying for planning permission you should provide the following documents to support your application:

  • Kent Biodiversity Gain Statement
  • any ecological surveys/assessments that would normally be required
  • map showing baseline habitats on your development site
  • map showing habitats after BNG has been implemented on the development site
  • statutory metric tool calculation (in Excel format)

If available, you should also provide your:

Discharge of conditions/legal agreement (s106)

If your application is approved, you will have planning conditions or a legal agreement (s106) to ensure the delivery and monitoring of the BNG you have committed to, over a 30-year period. This may be through a HMMP.

If you enter into a s106, a charge will be made to cover the costs of ongoing monitoring and review by us. We will monitor if the BNG strategy is being successfully delivered and take enforcement action if it is not.

You will also need to submit a Biodiversity Gain Plan to discharge the statutory condition under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021).

You can use the Biodiversity Gain Plan template to show how a development will achieve BNG.

When you submit your gain plan, you also need to provide your:

  • completed statutory biodiversity metric calculation
  • a compensation plan (if the development impacts irreplaceable habitats)
  • pre-development and post-development plans (showing the location of on-site habitat, the direction of north and drawn to an identified scale)