Chalk Stream Logo Min Aspect Ratio 1200 400

Biodiversity Net Gain Guidance

This guidance has been developed by Kent County Council to provide applicants with consistent advice across Kent and Medway. Please use the drop down menu below to expand guidance on each topic relating to Biodiversity Net Gain.

Local Planning Authorities may develop individual approaches to Biodiversity Net Gain which will be set through local planning policy and guidance notes. It is therefore recommended that you confirm any local requirements with the relevant planning authority at the beginning of scheme design.

Some of the guidance included on this page has been developed by summarising national level guidance and more detail on these issues can be find via the links to national guidance.

For other issues, such as defining strategic significance categories and ‘significant on-site gains’ an approach for Kent and Medway has been developed.

This guidance page will continue to be updated. Please contact if you have any queries regarding the guidance on this page or to request additional guidance.

Introduction to Biodiversity Net Gain:

  • What is Biodiversity Net Gain?

    What Is BNG

    Biodiversity Net Gain (BNG) is an approach to development, and/or land management, that aims to leave the natural environment in a measurably better state than it was beforehand. It uses a Metric based approach to predict the net change in biodiversity value that will occur as a result of development or a change in land use.

  • How is BNG measured?

    BNG habitats are used as a “proxy for biodiversity”. In practice this means that habitats present within the developments red line boundary are assigned a score (termed “Biodiversity Unit” according on their importance for biodiversity. The developer then calculates how many Biodiversity Units will be generated post-development, accounting for both losses of habitat to the development footprint and habitats created enhanced through the landscaping strategy.

    The method of calculating the number of Biodiversity Units for each habitat type has been set by DEFRA and is clearly defined through the Statutory Biodiversity Metric.

  • How can BNG be achieved by development?
    Some developments will be able to achieve the required uplift in BNG within the red line boundary (Figure 2). These developments are described as delivering all of their BNG “on-site”.



    Figure 2: A simplified illustration of how a development could achieve a net gain in biodiversity using only habitat creation and enhancement within the development site.

    Due to other constraints developments may not be able to achieve the required uplift in BNG within the red line boundary (Figure 3) and are therefore required to create or enhance habitat “off-site” (Figure 4).

    Net Loss

    Figure 3. A simplified illustration of a development which has resulted in a net loss of biodiversity within the development site. This could be due to other constraints on the development site.


    Offsite Net Gain

    Figure 4. The same simplified illustration of a development as in Figure 3, but with the addition of habitat creation a habitat creation and enhancement being delivered at an “off-site location”.

    Where it can be demonstrated that is not possible to achieve the required uplift in biodiversity through habitat creation through either on-site or off-site BNG then developers may purchase “Statutory Biodiversity Credits”. These credits can be purchased from the government, with revenue from their sales being used for habitat creation and enhancement schemes across the UK (not necessarily in Kent).


  • From when do developments need to deliver BNG?

    The commencement order sets out that the provisions of the Environment Act (2021) come into force on 12th February 2024. This means that from this date major developments (that do not meet the exemption criteria) must deliver BNG. There is a temporary exclusion for small developments until 2nd April 2024. Implementation for Nationally Significant Infrastructure Projects (NSIPs) is planned for 2025.

    It is important to note that the mandatory BNG requirement applies to applications submitted on these dates, not validated.


    When BNG

  • What exemptions apply for BNG?

    Not every major and small development will be required to deliver BNG. A set of exemption are set out by regulations.

    Exemptions as set out in The Biodiversity Gain Requirements (Exemptions) Regulations 2024

    • Temporary exemption for small developments until 2nd April 2024.
    • The biodiversity gain planning condition does not apply in relation to a section 73 planning permission where the original planning permission was exempt (e.g. original planning permission was submitted prior to 12th February 2024).
    • De minimis exemption:
      • No impact on priority habitat
      • Development impacts less than 25 square metres of onsite habitat, with a biodiversity metric value greater than zero.
      • Less than 5m of linear habitat on site.
    • Householder applications
    • High Speed Railway Transport Network
    • Planning permission required to deliver a consented BNG scheme.
    • Self-build and custom build applications (where there are no more than 9 dwellings, on a site no larger than 0.5ha, consists exclusively of self-build or custom housebuilding).
  • What is a 'major development'?

    ‘Major Development’ is defined as per as defined in article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015.

    “Major development” means development involving any one or more of the following:

    (a) the winning and working of minerals or the use of land for mineral-working deposits;

    (b) waste development;

    (c) the provision of dwellinghouses where—

      1. the number of dwellinghouses to be provided is 10 or more; or
      2. the development is to be carried out on a site having an area of 0.5 hectares or more and it is not known whether the development falls within sub-paragraph (c)(i);

    (d) the provision of a building or buildings where the floor space to be created by the development is 1,000 square metres or more; or

    (e) development carried out on a site having an area of 1 hectare or more


  • What is a 'small development'?

    ‘Small developments’ are those that do not fall into the category of a major development above.

    Small developments include the following:

    • residential development where the number of dwellings is between 1 and 9, or if this is unknown, the site area is less than 0.5 hectares
    • commercial development where floor space created is less than 1,000 square metres or total site area is less than 1 hectare
    • development that is not the winning and working of minerals or the use of land for mineral-working deposits
    • development that is not waste development
  • Who can calculate BNG?

    The User Guide for the Statutory Biodiversity Metric sets out that the BNG assessment must be undertaken by a ‘competent person’. A competent person is described as someone who “has the knowledge and skills to perform specified tasks to complete and review biodiversity metric calculations. You obtain this through training, qualifications, experience, or a combination of them.”  The definition of competency in BNG is aligned with the British Standard ‘Process for designing and implementing biodiversity net gain (BS 8683:202)’. There is an additional requirement for river assessments.

  • How is BNG applied to different types of planning application?

    BNG should be calculated for both Outline and Full applications. BNG calculations shall also be resubmitted for any reserved matters application or material amendment that is likely to affect BNG.

    Outline and phased applications will require additional biodiversity gain information that sets out how biodiversity gain will be achieved across the whole site on a phase-by-phase basis will be required for outline planning permissions and phased development. These applications will also be subject to a condition that requires a BNG Plan prior to commencement of each phase.

    Reserved matters will not be required to fulfil mandatory BNG if the outline was approved prior to mandatory BNG; it will only apply to new applications submitted after BNG is mandated (from 12th February 2024).

General Principles of Mandatory Biodiversity Net Gain: