Biodiversity net gain (BNG) is an approach to planning and land management that leaves the natural environment in a better state than it was before.
You must show that your proposals deliver biodiversity net gain.
You will need to understand the requirements of BNG if you are a:
- developer
- land manager
Contents:
- How BNG is measured and calculated
- Mandatory requirements and exemptions
- The BNG process
- Planning applications and BNG
- Other key principles and rules
- Guidance and advice
How BNG is measured and calculated
Under the Environment Act 2021, planning permissions granted in England, with a few exemptions, will have to deliver at least 10% biodiversity net gain, using the biodiversity metric to demonstrate this.
The Biodiversity Metric is used to calculate the value of all habitats within the development site (usually the red line boundary) for two scenarios; before and after development.
The current version of the metric is the statutory metric. The values of the habitats are measured in ‘biodiversity units’.
GOV.UK provide statutory biodiversity metric tools and guides.
The pre-development number of biodiversity units is compared to the post-development number of biodiversity units to assess if net gain is achieved.
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 Biodiversity Units of at least 10% as a result of the development process.
Mandatory requirements and exemptions
BNG applies to both major and minor development with some exceptions.
Definition of a minor development
For residential, minor developments are those:
- 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
- where the number of dwellings to be provided is not known, a site area of less than 0.5 hectares
For non-residential, 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
Exemptions
The biodiversity gain condition does not apply to the following types of development:
- development impacting habitat of an area below a threshold of 25 square metres - for example, five metres by five metres
- householder applications
- biodiversity gain sites - where habitats are being enhanced for wildlife
- small scale self-build and custom housebuilding
The BNG process
The Environment Act 2021 makes all planning permissions 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.
BNG can be delivered:
- on site – by creating or enhancing habitats to generate additional biodiversity units within the red line boundary of the development site.
- off site – by creating or enhancing habitats to generate additional biodiversity units outside the red line boundary of the development site.
- via Statutory biodiversity credits – by paying to purchase biodiversity credits from the UK Government’s credit sales service. Two credits will be required for every one unit to be compensated for.
- via a combination of the above
The national biodiversity credits purchase system outlines credit prices. It is designed for developments unable to meet their biodiversity net gain requirements locally.
National biodiversity credits are a last resort and will be much more expensive than securing biodiversity units more locally.
We will need evidence that all reasonable efforts have been made to buy the additional habitat creation locally.
Planning applications and BNG
There are national validation requirements set by the UK Government and outlined in the GOV.UK Biodiversity Net Gain Planning Practice Guidance.
These requirements are set out in the application form that you need to submit to us when applying for planning permission.
The requirements are:
- correctly completed application form
- completed statutory biodiversity metric or small sites metric, GOV.UK guidance on statutory biodiversity metric tools and guides
- statement: Confirming if the biodiversity value of the on-site habitat is lower on the date of the application (or earlier date) because of degradation/result of ‘trashing’ in which case the value must be immediately before degradation and evidence to support this
- description of any on-site irreplaceable habitats: on land to which the application relates and exists on the date of application
- plan (at a recognised scale): with North identified showing on-site habitat on the date of application including irreplaceable habitat. This should be shown within the red outline, not blue, on the site location plan
The metric will be subject to validation. If the following rules are not met the application may not be validated.
The metric must:
- be supplied as an Excel spreadsheet - screenshots or PDF versions will not be acceptable
- be supplied with all start page details filled out – ‘completed by’, ‘date of completion’
- have ‘the Statutory Biodiversity Metric’ as the ‘Start’ tab title
- be supplied with no input error/rules and principles not met flags (i.e. red boxes) after Row 10 on the ‘On-Site Habitat Baseline’ tab
- report the same site area as the application form and supplied redline boundary
All condition assessment sheets used to complete the metric must be supplied with the metric tool.
Guidance on completing the strategic significance drop-down within the statutory biodiversity metric
Strategic significance is defined by the Biodiversity Metric User Guide as “the local significance of the habitat based on its location and habitat type”.
Planning applicants and BNG unit providers must complete the strategic significance drop-down for each habitat parcel within all three modules of the Statutory Biodiversity Metric.
Until Cumbria’s Local Nature Recovery Strategy is published in March 2025, planning applicants and BNG unit providers must have regard to our Strategic Significance Guidance (PDF , 611KB).
The Strategic Significance Guidance must be used in conjunction with the Cumbria Local Nature Recovery Network interactive map when completing the strategic significance drop-down within all three modules of the Statutory Biodiversity Metric.
Other key principles and rules
The mitigation hierarchy
The biodiversity metric has been designed to discourage the loss of better-quality habitats to development, by making them significantly more expensive to provide net gain for compared to lower value habitats.
You should have regard to the rules and principles set out in the current version of the biodiversity metric user guide as these will be used to assess biodiversity statements and gain plans.
Where evidence is required to demonstrate compliance with the metric rules and principles (for example evidence of competency) this is provided within the biodiversity statement and/or gain plan.
Biodiversity net gain 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.
Other statutory legislation
Statutory obligations in relation to biodiversity include compliance with legislation relating to the protection of site, protection of species and preventing the spread of invasive non-native species including. The main legislation being:
- the Conservation of Habitats and Species Regulations 2017 (as amended)
- Wildlife and Countryside Act 1981 (as amended).
Advance site clearance
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.
This is mandated within Schedule 14 of the Environment Act where 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 biodiversity net gain.
Guidance and advice
Further information on BNG is available from: