Biodiversity Net Gain Update for Agents and Developers

You may be aware of biodiversity net gain (BNG). This is an approach to development that aims to leave the natural environment in a measurably better state than it was beforehand.

The Biodiversity Metric is a way of quantifying this. Natural England have published a free biodiversity accounting tool in Microsoft Excel format, which is to be used for the purposes of calculating biodiversity net gain.

It is not the Government’s intention for Local Authorities to produce their own guidance on how to use the Biodiversity Metric and achieve net gain as this will all be set out nationally. However, once this is available, we will be working with Northumberland County Council to produce a Northumberland wide  Supplementary Planning Document (SPD). This will support Local Plan Policies ST1 and DM10 and set out Northumberland-specific requirements.

Achieving 10% net gain means fully compensating for losses of habitat on a development site, but then going further so that overall there is a gain in habitat of at least 10% as a result of the development process. The Government is introducing this requirement to help meet its aspiration to leave the environment in a better state than it found it, and to help meet targets for nature recovery required under the Environment Act.

1. BNG will be mandatory from November 2023 for major development

Under the Environment Act 2021, all planning permissions granted in England (with a few exemptions) will have to deliver at least 10% biodiversity net gain, using a metric developed by DEFRA that generates a biodiversity value for a site before and after development to demonstrate this. This applies to major development from November 2023 and minor development from April 2024. Minor development means:

(i) For residential: where the number of dwellings to be provided is between one and nine inclusive on a site having an area of less than one hectare, or where the number of dwellings to be provided is not known, a site area of less than 0.5 hectares.

(ii) For non-residential: where the floor space to be created is less than 1,000 square metres OR where the site area is less than one hectare.

The following types of development will be exempted from BNG requirements:

  • development impacting habitat of an area below a ‘de minimis’ threshold of 25 metres squared, or 5m for linear habitats such as hedgerows
  • householder applications
  • biodiversity gain sites (where habitats are being enhanced for wildlife)
  • small scale self-build and custom housebuilding
One of the Parks haymeadow habitats

2. How the process will work

The Environment Act amends the Town and Country Planning Act to make all planning permissions (other than exempted ones) subject to a pre-commencement condition requiring the submission of a plan that demonstrates how 10% net gain will be achieved. The management of the habitat created to achieve this must then be secured by legal agreement for a minimum period of 30 years.

The habitat creation required to achieve 10% net gain can be undertaken on the development site itself if space and circumstances allow, on a separate site or a mixture of the two. Offsite habitat creation can be undertaken on land owned by the developer, or on third party land where the landowner is willing to undertake such work and maintain it for at least 30 years in return for a payment from the developer. It is anticipated that a market will develop in the provision of such sites. As a last resort the Government intends to introduce a national credits purchase system for developments unable to meet their BNG requirements locally.

Northumberland National Park Authority are looking to make offsite BNG units available for developers to purchase on our own land. The details (or price) has not been finalised yet, but a study published by DEFRA last year anticipates that prices are likely to be around £20,000 – £25,000 per unit. The Authority intends to discuss with other landowners who are considering entering this market.

3. Information to be submitted with a planning application

The BNG process is built around a pre-commencement condition, which is when the full details of the metric calculations and of the measures to be taken to secure 10% net gain are required. However, enough information will be required at determination stage for the LPA to be satisfied that a suitable net gain solution exists for that development.

We await further guidance from Government about this, but it is likely to be most straightforward to submit all required information with the planning application whenever possible, so that discharge of the BNG condition can follow on immediately after determination. The metric calculations and associated reporting as well as the development of habitat creation to achieve net gain will need to be undertaken by an experienced Ecologist.

Bellcrag flow peat bog
Bellcrag flow, a mire or blanket bog in Wark Forest, Northumberland National Park, England. OS grid reference NY 777 726

4. BNG does not replace existing legislation and policy

The BNG process simply introduces a quantitative framework for securing and demonstrating net gain. It does not replace the requirement to carry out a qualitative assessment of impacts on biodiversity through an Ecological Impact Assessment (EcIA). When a planning application is received by Northumberland National Park the Assessment will first be reviewed and assessed, before there is any consideration of a submitted metric in accordance with the mitigation hierarchy. Where there is the potential for impacts on European sites, the LPA will still need to undertake a Habitats Regulations Assessment.

Compliance with a number of other environmental planning policies will still need to be demonstrated by the developer; these include requirements relating to:

  • protected or important nature conservation sites
  • protected or important species
  • irreplaceable habitats

BNG maintains the mitigation hierarchy of avoiding impacts first, then mitigating and only compensating as a last resort. It cannot be used to bypass the mitigation hierarchy.

5. Planning for BNG early in your development planning

The Biodiversity Metric has been designed to disincentivise the loss of better-quality habitats to development, by making them significantly more expensive to provide net gain for compared to lower value habitats.

Consequently, it is important to establish the baseline value of a site at as early a stage as possible when considering its development potential, as the loss of higher value habitats may make a scheme unviable, or may require that parts of the site are safeguarded from development to enable an economically viable scheme to be developed.

A view of Shillmoor Farm, Green Side and Pass Peth
Shillmoor Farm, Green Side and Pass Peth, Northumberland National Park, England

6. Clearing sites in advance

Within Schedule 14 of the Environment Act measures have been included that allow the Local Planning Authority to take account of any habitat degradation or destruction undertaken on a site since January 2020, and to take the earlier habitat state as the baseline for the purposes of biodiversity net gain. This is to ensure that there is no advantage to be gained by the deliberate clearance of land in order to achieve a low baseline value for BNG.

If habitats on site have been destroyed or degraded prior to a survey and submission of planning application, the earlier habitat state will be taken as the baseline for the purposes of the biodiversity metric and a habitat condition score of ‘good’ will be allocated to the habitat parcel as a precaution.

Further information

You can find further information at the external links below:

Natural England Biodiversity Net Gain Brochure

Biodiversity Net Gain: Good Practice Principles for Development – a Practical Guide


Future Homes Hub: Biodiversity Net Gain Project

Biodiversity Net Gain Metric and User Guide

To discuss Northumberland National Park Authority’s approach to biodiversity net gain

please contact Susannah Buylla, Head of Planning & Policy, email: