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Biodiversity net gain (BNG) - The basics

What is biodiversity?

Biodiversity is the variety of life found in an area.

This includes:

  • Animals,
  • Plants,
  • Fungi, and
  • Micro-organisms.

What is a net gain?

A net gain is an overall increase in something.

What is Biodiversity net gain?

Biodiversity net gain means the increase in biodiversity in an area.

Why does this matter?

Biodiversity net gain is important.

  • It allows development and land management to have a positive impact on nature.
  • It leaves the natural environment in a better state than it was before.
  • It does this by enhancing, creating, and increasing habitats on the site.
  • This should increase the wildlife in the area.

Do I need to understand Biodiversity net gain?

You will need to understand the requirements of BNG if you are a:

  • Developer
  • Land Manager
  • Local Planning Authority

Development planning in Darlington

In Darlington we are securing areas for use as offsite habitat creation. This will increase biodiversity within the borough.

These areas are managed and monitored for a 30-year period.

Our Local Plan (2016 – 2036) requires any new planning development to show a biodiversity net gain. This is in-line with our Local Plan policies and with government legislation. 

However, from 12th February 2024 there is a legal requirement for at least a 10% increase in biodiversity for large sites. From 2nd April 2024 this will also cover small sites.

This means that developers must increase biodiversity levels to a minimum of 10% to secure planning permission. Without it, we will decline planning permission. Habitats will need to be protected, managed, and monitored for a period of 30 years.

We expect the use of the new Statutory Biodiversity Metric to calculate the biodiversity onsite prior to development and after development.

Be aware that BNG does not replace the need to carry out other assessments for protected species or habitats. Protected species and habitat surveys will still be required, and any mitigation, compensation, or enhancement will still be required before biodiversity net gain is considered.

The authority will also still need to undertake a Habitats Regulations Assessment if there there may be impacts on European protected sites, such as:

  • Special Areas of Conservation, or
  • Special Protection Areas,

How we measure BNG

The government has produced the Statutory biodiversity Metric.

This helps developers to calculate a minimum 10% gain on the pre-development biodiversity value of the site.

The Metric calculates Biodiversity Units based on the habitats present on site, or habitats to be created or enhanced.

Achieving 10% net gain means compensating for losses of habitat on a development site. Then increasing Biodiversity Units to least 10% on top of the original site. 

The Environment Act 2021 makes all planning permissions subject to a pre-commencement condition requiring the submission of a Biodiversity Gain Plan that shows how 10% net gain will be achieved.

The management of the habitat created to achieve the gain must then be secured by legal agreement for a minimum period of 30 years. 

What does BNG apply to?

With a few exemptions all planning permissions granted in England will have to deliver at least 10% BNG after the 12th February for major applications and 2nd April for minor applications..

The biodiversity Metric to is used to demonstrate this.

BNG applies to all land development to low water mark, except permitted development, which includes:

  • Brownfield development.
  • Change of use applications.
  • Temporary permissions.
  • Small sites/minor development – see below.

Preparing for Biodiversity Net Gain early in your development planning

The BNG Metric discourages the loss of better-quality habitats to development.

It makes it much more expensive to provide net gain for high value habitats compared to lower value habitats.

It is important to check habitats within a site as early as possible when considering its development potential.

The loss of higher value habitats may make a scheme non-viable or may require that parts of the site are safeguarded from development.

Habitat creation credits

It is not always possible to create a habitat on a development site.

  • If this is the case, we can sometimes create habitats elsewhere in the local area.
  • If this is not possible, the Government has a system which allows developers to buy credits.
  • The credits are used to create habitats at a different location.

Developers can only buy credits once all other options for habitat creation, onsite and offsite, are exhausted.

Options for delivery of Biodiversity Net Gain


All land within the boundary of a project. In a planning context, this usually means within a red line boundary. 


Land outside of the on-site boundary, regardless of ownership.

Any site delivering ‘off-site’ biodiversity units must be registered on the Natural England ‘biodiversity gain site register’.

A legal commitment is required to create habitat enhancements and maintain them for at least 30 years after completion of the enhancements. 

Statutory credits

The government has introduced Statutory Biodiversity Credits.

They can be purchased by developers to allow developments which are unable to meet their Biodiversity Net Gain on-site or off-site.

Credit sales revenue will be received by Natural England and invested in habitat creation projects.

Statutory Biodiversity Credits are a last resort. They will be much more expensive than securing Biodiversity Units more locally.

Important information

If you buy statutory biodiversity credits, a ‘spatial risk multiplier’ will apply.

This doubles the number of credits you need.

  • You must buy 2 credits for every 1 biodiversity unit you need to compensate for.
  • The statutory biodiversity metric will automatically calculate this multiplication for you.


Minor developments are those:

  • Where the number of dwellings to be provided is between one and nine on a site having an area of less than one hectare.
  • Where the number of dwellings to be provided is not known, a site area of less than 0.5 hectares.


Minor developments are those:

  • Where the floor space to be created is less than 1,000 square metres.
  • Where the site area is less than one hectare.
  • Types of developments exempt from Biodiversity Net Gain requirements.
  • Development impacting non-priority habitat of an area below a ‘de minimis’ threshold of 25 square metres - for example, 5 metres by 5 metres.
  • Householder applications.
  • BNG - where habitats are being enhanced for wildlife.
  • Small scale self-build and custom housebuilding.

Clearing sites in advance

As of January 2020, Schedule 14 of the Environment Act lets us take any habitat degradation or destruction into account.

We take the earlier habitat state as the baseline for the purposes of Biodiversity Net Gain.

This is to make sure there is no advantage gained by the deliberate clearance of land to achieve a low baseline value for Biodiversity Net Gain.

If habitats on site are destroyed or degraded before a survey and submission of planning application, the earlier habitat state will be taken as the baseline for the purposes of the biodiversity Metric.

A habitat condition score of ‘good’ is allocated to the habitat parcel as a precaution.

Further information for what to submit to planning will be updated shortly. In the meantime, please visit the following Government guidance on BNG:

Draft biodiversity net gain planning practice guidance [external link]

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