What is Biodiversity Net Gain?

Biodiversity net gain (BNG) is an approach to development that aims to leave the natural environment in a measurably better state than was present beforehand. Improvements for biodiversity are made by creating or enhancing habitats in association with development and only applies to habitats, such as grassland, hedges, and watercourses. It can be achieved on-site, off-site or through a combination of on-site and off-site measures.

Measurable gains and losses must be quantified using the DEFRA Statutory Biodiversity Metric. The metric is an Excel based tool that uses type, condition, and area of habitats as a proxy for change in biodiversity from before to after a development, in terms of ‘Biodiversity Units’ (BUs). The difficulty of enhancing an existing habitat or creating a new habitat, as well as the time taken to do so, are factored into the metric calculation.

Development will need to show a minimum 10% increase in BUs, compared to the baseline, to demonstrate that BNG can be delivered. It is important to remember that BUs derived using the metric are only a proxy for biodiversity and additional ecological data must be used to design BNG based on sound ecological practices. Each habitat type present on development site (areas, hedges, and watercourse) must achieve a 10% uplift in value. You must legally secure all off-site gains or significant on-site gains for at least 30 years.

BNG is additional to, and does not replace, existing wildlife legislation, policy, and guidance, e.g., Environmental Impact Assessment (EIA), Habitats Regulation Assessment (HRA) etc.  Therefore, development proposals will still be subject to the same biodiversity assessment criteria for designated sites and protected species.

The BNG framework, national, county, and local policy is an evolving landscape, and this guidance will be subject to updates. It is recommended to always refer to  the most up to date guidance..

GOV.UK biodiversity net gain planning practice guidance sets out the framework of how BNG will be applied in the planning process. The Devon County Council website also provides guidance for applications made in Devon and should be followed, unless stated otherwise.

Mandatory Biodiversity Net Gain (BNG)


In England, biodiversity net gain (BNG) is required under a statutory framework introduced by Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. This is referred to as biodiversity net gain in Planning Practice Guidance to distinguish it from other or more general biodiversity gains.

Mandatory BNG is in addition to existing policy requirements and must follow the statutory framework for BNG. All applicable developments must deliver a minimum 10% BNG and this requirement cannot be disapplied, e.g., using a Section 73 amendment. The 10% gain is required in legislation and therefore there is no scope for LPAs to allow a reduction on viability grounds.

BNG should be considered early in the planning process to ensure it is factored into site selection and design, as well as considering survey windows which are seasonally dependent.  Applicants are encouraged to use the Council’s Pre-application Advice Service to further understand the specific requirements in relation to their site.

Does mandatory BNG requirement apply to my application?

From 12 February 2024 all major planning applications consented in England will be deemed subject to the general biodiversity gain condition to secure the biodiversity gain objective. This objective is to deliver at least a 10% increase in relation to the pre-development biodiversity value of the development granted permission. BNG will become mandatory for minor development sites on 02 April 2024 and is expected to extend to Nationally Significant Infrastructure Projects (NSIPs) from late November 2025.

The general biodiversity gain condition will not apply to extant permissions or those submitted prior to the commencement date. Current BNG policy in Cranbrook and those within applicable Neighbourhood Plans will still apply until the mandatory framework commences.

Certain types of development, e.g., based on de minimis exemptions, are exempt from the need to comply with the general biodiversity gain condition as set out in the Biodiversity Gain Requirements (Exemptions) Regulations 2024. The current East Devon Local Plan and National Planning Policy Framework (NPPF) require development proposals to deliver ecological enhancement, irrespective of biodiversity net gain (BNG) requirements.

Validation requirements

Applicants must confirm whether they believe that planning permission, if granted, would be subject to the biodiversity gain condition, and if not, the reasons why. This is a new national mandatory validation requirement.

Typical exemptions include all householder applications, certain self-build developments, and de minimums exemption.

Where development would be subject to the general biodiversity gain condition, the application must be accompanied by minimum information set out in Article 7A of the Town and Country Planning Act 1990. For  avoidance of doubt, the following is the mandatory minimum information required:

  • a statement as to whether the applicant believes that planning permission, if granted, would be subject to the biodiversity gain condition;
  • the pre-development biodiversity value of the onsite habitat on the date of application (or an earlier date) including the completed metric calculation tool used showing the calculations, the publication date and version of the biodiversity metric used to calculate that value;
  • where the applicant wishes to use an earlier date, the proposed earlier date and the reasons for proposing that date;
  • a statement confirming whether the biodiversity value of the onsite habitat is lower on the date of application (or an earlier date) because of the carrying on of activities (‘degradation’) in which case the value is to be taken as immediately before the carrying on of the activities, and if degradation has taken place supporting evidence of this;
  • a description of any irreplaceable habitat (as set out in column 1 of the Schedule to the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations [2024]) on the land to which the application relates, that exists on the date of application, (or an earlier date); and
  • a plan, drawn to an identified scale which must show the direction of North, showing onsite habitat existing on the date of application (or an earlier date), including any irreplaceable habitat.

If this information has not been provided, the local planning authority must refuse to validate the application. Within the planning application form, applicants will be asked to confirm whether this information accompanies the application. Where these details have been provided elsewhere in accompanying documents, applicants are encouraged to refer to these rather than duplicate this information within the application form.

In addition to these minimum requirements, further information may be required to assist the consideration of biodiversity net gain as part of the planning application, to enable decision makers to consider whether the general condition is capable of being successfully discharged following approval. For example, where there are considerations around significant onsite biodiversity enhancements or use of offsite biodiversity units, a  draft Habitat Management and Monitoring Plan (HMMP), completed draft metric demonstrating whether proposed net gain proposals are likely to be achievable, and details of all off-site habitats may be required. Specific further requirements will be set out in the Local Validation Checklist which is subject to change.

If planning obligations are going to be used, it is good practice to submit information about any potential planning obligations connected to the application.


The statutory framework for biodiversity net gain involves the discharge of the general biodiversity gain condition following the grant of planning permission to ensure the objective of at least 10% net gain will be met for a development. The determination of the Biodiversity Gain Plan (BGP) is the mechanism to confirm whether the development meets the biodiversity gain objective. Development may not commence until the BGP is approved.

Biodiversity Gain Plan

The Biodiversity Gain Plan sets out how the biodiversity gain objective of at least a 10% gain will be met for the development granted planning permission. It must contain the relevant information  to enable the planning authority to determine whether the biodiversity gain objective has been met.

This must be submitted no earlier than one day after permission has been granted and must be approved by East Devon District Council to discharge the general biodiversity gain condition. For ease of use and to ensure all relevant information is submitted, the applicant is encouraged to use the Biodiversity Gain Plan template.

It is recommended that a draft BGP is submitted with planning submission to ensure they have been considered at an early stage and to minimise potential delays with discharging the general biodiversity gain condition.

Habitat Management and Monitoring Pan

A habitat management and monitoring plan (HMMP) is required to specify the management and monitoring information for any significant on-site enhancements and off-site gains. Similar to a Landscape and Ecological Management Plan (LEMP), a HMMP will give a detailed schedule of how the applicant  plans to create and enhance habitats for biodiversity net gain (BNG) in addition to how they  plan to manage and monitor the habitat for at least 30 years. The level of detail within the HMMP should be proportionate to the scale of works and provide sufficient confidence in its delivery. The Natural England HMMP template is recommended to ensure  consistency. 

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