Biodiversity Net Gain Guidance


What is Biodiversity Net Gain? 

As defined by Natural England, “Biodiversity Net Gain (BNG) is an approach to development, land and marine management that leaves biodiversity in a measurably better state than before the development took place”. It aims to create new habitats and enhance existing habitats, ensuring ecological connectivity is retained and improved across England. BNG does not supersede, replace, or in any way reduce or undermine existing statutory and policy protections and requirements relating to wildlife, habitats, protected species, protected sites, or irreplaceable habitat.


What Does Biodiversity Net Gain Mean for New Development?

Major Development

From the 12 February 2024, all major development (sites of 10 dwellings/0.5 hectares or more, or non-residential development of 1000 square metre floorspace/1 hectare or more) will have to deliver at least 10% BNG.

BNG does not apply to retrospective planning permissions made under S73 of the Town and Country Planning Act 1990, or S73 permissions where the original permission was granted before 12 February 2024 or the application for the original permission was made before 12 February 2024.

Small Sites

From the 2 April 2024, BNG will be required for small sites. These are defined as:

  • Residential development where the number of dwellings is between one and nine, 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.

Nationally Significant Infrastructure Projects (NSIPs)

BNG is expected to be a requirement for NSIPs from late 2025.



The Biodiversity Gain Requirements (Exemptions) Regulations 2024 specify exemptions for categories of development to which BNG legislation does not apply. These are outlined in the below sections.

Below Threshold

Development that does not impact a Priority Habitat identified by the Natural Environment and Rural Communities (NERC) Act 2006 and impacts less than:

  • 25 square metres (5 metres by 5 metres) of habitat.
  • 5 metres of linear habitats, such as hedgerows.

Householder Applications

These are applications made by householders as defined within Article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015. It includes, for example, small projects such as home extensions, conservatories, or loft conversions.

Self-Build and Custom Build Applications

An exemption applies to this type of development when all the following conditions apply:

  • It consists of no more than nine dwellings.
  • It is on a site that has an area no larger than 0.5 hectares.
  • It consists exclusively of dwellings that are self-build or custom housebuilding as defined in Section 1(A1) of the Self-build and Custom Housebuilding Act 2015.

Change of Use and Permitted Development

These applications are exempt.

Biodiversity Gain Site

Developments undertaken for the purpose of fulfilling the BNG planning condition for another development are exempt.

Irreplaceable Habitats

The Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024 outlines what is classified as irreplaceable habitat. These are as follows:

  • Ancient woodland.
  • Ancient and veteran trees.
  • Blanket bog.
  • Limestone pavements.
  • Coastal sand dunes.
  • Spartina Saltmarsh swards.
  • Mediterranean Saltmarsh scrub.
  • Lowland fens.

The irreplaceable habitats list recognises and protects England’s most valuable habitats. Bassetlaw supports approximately 600 hectares of ancient woodland, which is almost double the average woodland coverage for England and reflects the District’s historical association with Sherwood Forest.

Irreplaceable habitats are extremely difficult and often impossible to recreate, and therefore cannot achieve the requirement to increase biodiversity on top of no net loss. For BNG purposes, the 10% net gain requirement is not applied to irreplaceable habitats. Irreplaceable habitats must still be recorded within the Statutory Biodiversity Metric, but any impacts to these habitats will flag as unacceptable and require bespoke compensation to be agreed with the Council.


Statutory Biodiversity Metric

The Statutory Biodiversity Metric is the tool that measures the value of habitats by calculating the number of biodiversity units within a development red-line boundary. The formula calculates how many units a habitat contains before development takes place, and how many units are required to replace those lost from development to achieve at least 10% BNG.

To demonstrate you have accurately calculated the number of biodiversity units of existing habitat, or habitat creation and enhancements to achieve at least 10% BNG, applicants must use the Statutory Biodiversity Metric tool. Applicants will need to include all habitat that exists within the red-line boundary. This includes all features, whether they may be lost, retained, or improved.

Small Sites Metric

If a development qualifies as a small site, applicants can use a simpler version of the biodiversity metric called the Small Sites Metric (SSM). The SSM cannot be used on sites where 1) habitats that are not listed in the SSM are present, 2) if NERC Act Priority Habitats are located within the development site (excluding some hedgerows and arable field margins), or 3) where European Protected Species are present on the development site (e.g., great crested newts, bats).


Local Nature Recovery Strategy (LNRS)

LNRS can support a strategic approach to off-site BNG delivery, agreeing evidence-based locations to expand and connect existing habitat and provide wider environmental benefits.

Bassetlaw District Council will be supporting Nottinghamshire County Council, the responsible authority leading the production of the LNRS, in identifying land that can used for off-site BNG.

The LNRS is in the early stages of development. It is anticipated that it will be published in 2025. For more information go to the Nottinghamshire County Council website.


Interim Guidance on Strategic Significance

The LNRS will play a key role in BNG by determining the ‘strategic significance’ multiplier within the biodiversity metric. This mechanism means that there will be an incentive for developers to align with the LNRS when selecting the location of any off-site BNG units. Until the LNRS for Nottinghamshire has been formally adopted, the following criteria should be assigned when selecting the strategic significance of a habitat:

Strategic significance



  • Statutory designated sites for nature.
  • Local wildlife sites (LWS).
  • All trees in the public realm.
  • Habitats within 100 metres of statutory designated sites for nature or LWSs that are a qualifying feature of that site or are a NERC Act Priority Habitat.
  • Priority habitats and focal areas shown on the Trent Valley Biodiversity Opportunities Map.
  • High and very high distinctiveness hedgerows.
  • All rivers and streams.
  • Irreplaceable habitats.


  • Any NERC Act Priority Habitat that does not meet the criteria for high strategic significance.


  • All other habitats.


Minimum Information

In line with national requirements, applications subject to BNG must be accompanied by:

  • A statement whether the applicant believes that planning permission, if granted, would be subject to the biodiversity gain condition.
  • The pre-development biodiversity value of the on-site habitat on the date of application (or an earlier date) including the completed Statutory Biodiversity Metric showing the calculations, the publication date, and version of the metric used to calculate that value.
  • Where the applicant wishes to use an earlier date, the proposed earlier date and the reasons and justifications for proposing that date.
  • A statement confirming whether the biodiversity value of the on-site 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 on the land to which the application relates, that exists on the date of application, (or an earlier date).
  • A plan, drawn to scale which must show the direction of north, showing on-site habitat existing on the date of application (or an earlier date), including any irreplaceable habitat.

Applications that do not include the above information will not be validated.


Delivering Biodiversity Net Gain

There are three mechanisms to delivering BNG: on-site (within the red-line boundary), off-site (outside the red-line boundary), or through Statutory Biodiversity Credits (these are a last resort). A mixture of these three mechanisms can also be applied when delivering BNG. Applicants are informed that the Council supports a ‘local first’ approach in the delivery of BNG, hereby striving to ensure no community within Bassetlaw or Nottinghamshire is deprived of the benefits of nature’s recovery.


Biodiversity Gain Plan 

Post planning permission, the statutory framework for BNG involves the discharge of the general biodiversity gain condition by a post-permission document to ensure the objective of at least 10% net gain will be met for the development. Development may not commence until the Biodiversity Gain Plan is approved in writing by the Council. The Council therefore recommends a draft Biodiversity Gain Plan is submitted with the planning application.

As per national requirements, a Biodiversity Gain Plan must include:

  • Information about the steps taken or to be taken to minimise the adverse effect of the development on the biodiversity of the on-site habitat and any other habitat.
  • The pre-development biodiversity value of the on-site habitat.
  • The post-development biodiversity value of the on-site habitat.
  • Any registered off-site biodiversity gain allocated to the development and the biodiversity value of that gain in relation to the development.
  • Any biodiversity credits purchased for the development.

In addition, the following specified matters are required where development is not to proceed in phases:

  • Name and address of the person completing the Biodiversity Gain Plan, and (if different) the person submitting the document.
  • The reference number of the planning permission to which the plan relates.
  • A description of the development to which the plan relates.
  • The completed Statutory Biodiversity Metric calculation tool, showing the calculation of the pre-development and post-development biodiversity value.
  • A description of arrangements for maintenance and monitoring of habitat enhancement for at least 30 years after the development is completed (in cases where there is no irreplaceable habitat on the development site).
  • How the Biodiversity Gain Hierarchy will be followed and where any actions in that hierarchy are not followed, the reason for that.
  • The relevant date for the purposes of calculating the pre-development biodiversity value of on-site habitats.
  • Pre-development and post-development plans showing the location of on-site habitat and drawn to an identified scale and showing the direction of north.

The allocation of any off-site biodiversity gains must be recorded on the biodiversity gain sites register before the Council can approve your biodiversity gain plan.

Although the Biodiversity Gain Plan is a post-permission document, the Council reserves the right to request detailed information at the application stage to ensure the biodiversity strategy is capable of being discharged.


Securing BNG

The mechanism, financial arrangement, and responsible party for the delivery, management, and monitoring of BNG will be appropriately secured through planning conditions, Section 106 planning obligation, or in exceptional circumstances a Conservation Covenant with an approved DEFRA responsible body.

Management and Monitoring

Applicants should submit a Habitat Management and Monitoring Plan (HMMP) to demonstrate how you will manage and monitor habitat creation and/or enhancements for the 30-year legacy. You will be required to submit your HMMP with your Biodiversity Gain Plan if making significant on-site or off-site biodiversity gains, however the Council encourages applicants to submit this plan with their planning application using Natural England’s published HMMP template.

The Council also has responsibilities in relation to monitoring BNG compliance with planning conditions and enforcement of triggers within Section 106 planning obligations where it is party to them. As well as reviewing submitted HMMP monitoring reports, the Council can undertake site monitoring to verify delivery of BNG and submitted monitoring details. Where there are breaches, the Council can utilise enforcement powers when necessary.

The Council’s monitoring fee will vary on a project-by-project basis and will consider factors such as the biodiversity gain site size, habitat distinctiveness, target condition, and administrative costs. The monitoring fee will be required as an upfront payment and will be agreed in the relevant Section 106 planning agreement.

Last Updated on Monday, April 8, 2024