Biodiversity Net Gain – A Practical Summary

by Adam Willson

19 March 2024

Biodiversity Net Gain (“BNG”) requires developers to show that their proposed development plans not only replace any existing habitats that are lost by the development, but also give at least a 10% gain on what was lost.

The ‘gain’ will be judged according to a metric prepared by the Department for Environment, Food & Rural Affairs. See Calculate biodiversity value with the statutory biodiversity metric – GOV.UK ( for more details.

The intention behind the requirement is to ensure that habitats for wildlife are left in a measurably better state than they were prior to any development.

Developers will need to be conscious to appropriately plan for and deliver BNG in any development opportunity, otherwise they will be unable to bring the development forward.

Mandatory Requirement?

The mandatory requirement took effect on 12 February 2024 for most types of developments/permissions, with the exception of small sites (expected to be introduced from April 2024 onwards) and those which are exempt. The mandatory planning condition for BNG will not apply to planning permissions where that application in respect of that permission was made before 12 February 2024.

A small site is defined as:

For residential:

  • between 1-9 dwellings on a site having an area less than one hectare; or
  • where the number of dwellings to be provided is not known, on a site area of less than 0.5 hectares;

For non-residential:

  • where the floor space to be created is less than 1,000 square metres; or
  • where the site is less than one hectare.

It is also worth noting that a change of use can be caught by BNG, but if the site is already built on then it is likely it will be zero rated (as there are no habitats). However, if there are any habitats at all, then on a change of use a 10% gain will need to be provided.

What must a developer do?

During the planning application process the developer must submit a BNG statement, giving a general overview of the biodiversity impact and changes of the site, and then indicating what steps will be taken to minimise any adverse impact and to enhance biodiversity on-site (i.e. within the red line boundary of the plan submitted with the application).

The developer must be able to demonstrate a gain of at least 10% in biodiversity, though some local planning authorities may have policies requiring over 10% BNG. Generally these gains must be able to be delivered within 12 months of development.

BNG can be achieved by the following steps (which the developer must consider in order):

  1.  creating biodiversity on-site;
  2. if unable to achieve on-site, then a mixture of on-site and off-site (the off-site being either the developer’s own land outside the site or alternatively they can purchase off-site biodiversity units on the market); and
  3. if BNG cannot be achieved on-site or off-site, then the developer must buy statutory credits from the Government. However, this should be a last resort.

With the preference being for BNG on-site, developers would be wise to involve an ecological consultant to work alongside their architects and urban designers to see how best BNG can be achieved on-site and therefore avoid the need to purchase off-site units which are anticipated to be expensive (particularly statutory credits).

How BNG is enforced and secured

In the first instance if a local planning authority does not agree with a developer’s BNG plan then they will not grant planning permission.

Once the BNG is approved, the local planning authority will require BNG obligations to be secured for at least 30 years.

  • If the BNG gains are all on-site, then this can be achieved by way of a planning condition, or a legal agreement (i.e. S106 obligations or a Conservation Covenant).
  • If the BNG gains are to be off-site (in part or full) then they must be secured by either S106 obligations or a Conservation Covenant.

S106 is the tried and tested means of local planning authorities securing planning requirements, and it is anticipated that in the short term this will be the preferred option with wording being included to cover off the requirements of BNG. These agreements are made directly between the local planning authority and the relevant BNG landowner and any breaches are enforceable by the local planning authority.

Conservation covenants are relatively new and require the relevant BNG landowner to enter into an agreement with a ‘responsible body’ for the purpose of securing land for BNG and other conservation purposes where necessary (such as nutrient or water neutrality). The responsible body effectively regulates and enforces the promises made by the landowner under the agreement. It is anticipated that these will be used when the relevant land is located outside of the local planning authority’s area.

How can we help?

Please contact us if you would like advice relating to BNG, including but not limited to:

  • Understanding how BNG may impact upon your proposed development plans;
  • Identifying opportunities as a developer to off-set your biodiversity requirements on a development site (via either land you own or third party sites);
  • Determining whether you should enter into a legal agreement to secure BNG as a third party owner and advising of the implications;
  • Securing BNG requirements (on-site or off-site) and where relevant putting in place the relevant agreement(s) to secure those requirements;



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