1.       The UK is one of the world’s most nature-depleted countries. The headline finding in the State of Nature Report 2023 told us that one in six species is at risk of extinction but this alarming figure obscures greater decline within certain taxonomic groups: 21% of plant species, 39% of vertebrates and 11% of fungi and lichens are classified as being at risk of extinction in Great Britain.[1]

2.       To counter this ecosystem loss the UK Government has introduced domestic legislation which seeks to restore or create 500,000 hectares of wildlife-rich habitats by the end of December 2042,[2] much of which will be achieved through Biodiversity Net Gain (“BNG”).

3.       BNG is an approach to development which requires an accompanying improvement in the status of wildlife habitats. While the policy has been a feature of the planning policy landscape for some time, it is now a mandatory requirement. Initially it applied only to major developments, but was extended on 2 April 2024 to cover all developments, with the exception of nationally significant infrastructure projects.[3]

What is the BNG requirement and how is it calculated?

4.       From 2 April 2024, every grant of planning permission – with a few exceptions discussed below – will be deemed to have been granted subject to a pre-commencement condition that the development delivers a biodiversity gain. The minimum gain is currently set at 10%,[4] and must be demonstrated through an approved Biodiversity Gain Plan (“BGP”).

5.       Amongst other things,[5] the BGP must demonstrate the site’s pre-development and post-development biodiversity value. This value is calculated using a standardised metric, which must also be submitted as part of the BGP.

6.       Those seeking to develop small sites may use a simplified Small Sites Metric (“SSM”) which, unlike the statutory biodiversity metric, does not have to be completed by an ecologist or similarly qualified person. However, applicants should be aware that there are some habitats for which the SSM may not be used; specifically, where priority habitats (including some hedgerows and arable field margins), protected sites, or European protected species are present.

7.       The person carrying out the SSM must be competent in identifying the habitats present on site pre-development, and also the management requirements for habitats to be created or enhanced post-development. Some applicants may, therefore, wish to seek expert advice when using the SSM to ensure that the process is carried out effectively. This is relevant, as local planning authorities may only approve a BGP where they are satisfied there is evidence that BNG of at least 10% will be met.[6]

How can BNG be achieved?

8.       BNG may be achieved through a range of interventions: on-site activities, off-site activities and the purchase of biodiversity credits. All three interventions can be combined, however, applicants for planning permission will be expected to follow the Biodiversity Gain Hierarchy (“BGH”), which permits compensation to be provided in the following order of priority: [7]

a.       On-site habitat enhancement

b.       On-site habitat creation

c.       Off-site habitat enhancement or creation

d.       Purchase of biodiversity credits[8]

9.       On-site BNG provision is likely to be the most cost effective solution for applicants wishing to bring forward small sites. It is, therefore, advised to build this provision into plans at an early stage.

10.   Applicants should be aware that the 10% BNG requirement does not apply to irreplaceable habitats.[9] In such habitats, paragraph 186 of the National Planning Policy Framework applies, and the planning situation becomes considerably more complex.

What constitutes a small development?

11.   Small developments are those which do not fall into the category of a major development, as defined in article 2(1) of the Town and Country Planning (Development Management Procedure)(England) Order 2015. In practice therefore, a small development means:

a.       residential development where the number of dwellings is between 1 and 9 on a site of an area 1 hectare or less, or if the number of dwellings is unknown, the site area is less than 0.5 hectares;

b.       commercial development where floor space created is less than 1,000 square metres or total site area is less than 1 hectare;

c.       development that is not the winning and working of minerals or the use of land for mineral-working deposits ;

d.       development that is not waste development.

Are there any exemptions from BNG requirements?

12.   Some developments are exempt from BNG regulations of which the following are likely to be of relevance to the developers of small sites:

De minimis development[10]

13.   Developments are exempt from BNG requirements if they are too minor to merit consideration. A development will fall below that threshold if it does not impact a priority habitat[11] and impacts less than 25 m2 of the on-site habitat (such as modified grasslands), or 5m of linear habitat (such as native hedgerows).

Householder developments[12]

14.   Applications relating to existing houses or for development within the curtilage of a house are exempt from the BNG requirements. However, applicants are advised to familiarise themselves with their local planning authority’s guidance on householder developments.

Self-build and custom-build development[13]

15.   Self- and custom build developments are defined as “the building or completion by individuals, associations of individuals, or persons working with or for individuals or associations of individuals, of houses to be occupied as homes by those individuals.”[14]

16.   Where those developments consist of no more than 9 dwellings, occupy a site no larger than 0.5 hectares, and consist exclusively of self- or custom-built houses, BNG does not apply.


17.   The potential for contributing positively to the enhancement and restoration of Great Britain’s natural habitats is to be welcomed. However, those looking to bring forward small developments will now have to grapple with BNG provisions. Applicants who have failed to consider BNG when putting together their planning applications risk expensive and time-consuming negotiations with local authorities when it comes to securing post-commencement approval for their BNP. It is therefore to be recommended that BNG provisions be considered at the outset of the development process, to prevent an unwelcome surprise later in the planning process.

[1] State of Nature Report 2023, https://stateofnature.org.uk/wp-content/uploads/2023/09/TP25999-State-of-Nature-main-report_2023_FULL-DOC-v12.pdf

[2] Environmental Targets (Biodiversity)(England) Regulations 2023, reg 7

[3] Section 90A and Schedule 7A of the Town and Country Planning Act 1990

[4] Town and Country Planning Act 1990, schedule 7A, para. 2(2)

[5] Town and Country Planning Act 1990, schedule 7A, para. 13(2); Town and Country Planning (Development Management Procedure)(England) Order 2015.

[6] Town and Country Planning Act 1990, schedule 7A, para. 15(2)(e)

[7] Articles 37A and 37D of the Town and Country Planning (Development Management Procedure) (England) Order 2015

[8] https://www.gov.uk/guidance/statutory-biodiversity-credit-prices

[9] Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024

[10] Biodiversity Gain Requirements (Exemption) Regulations 2024, regulation 4

[11] https://naturalengland-defra.opendata.arcgis.com/datasets/Defra::priority-habitats-inventory-england/about

[12] Biodiversity Gain Requirements (Exemption) Regulations 2024, regulation 6

[13] Biodiversity Gain Requirements (Exemption) Regulations 2024, regulation 8

[14] Housing and Planning Act 2016, section 9(1)

Anna Stein is now accepting instructions, having recently completed her first 6 months of pupillage at No5 Barristers’​ Chambers

Please contact Andrew Bisbey and Marc Forrest-Thomas for further information.