Biodiversity net gain information and guidance
Biodiversity net gain (BNG) is an approach to development that requires developments to be designed and planned in ways that leave the natural environment in a measurably better state than prior to development.
BNG is already required under policy ENV DM5 of the Arun Local Plan, which states all development schemes should, in the first instance, seek to achieve a net gain in biodiversity and protect existing habitats on site.
The Environment Act 2021 goes further, and since 12 February 2024, it is a mandatory requirement for all major developments (with a few exemptions) to deliver a net gain of at least 10%. Habitat management and monitoring must be secured for at least 30 years.
Since 2 April 2024, this requirement now applies to minor development, as per development definitions within the Town and Country Planning Act (1990).
BNG exemptions
A proposed development may be exempt from BNG for one or more of the following reasons:
- development is 'de minimis'. These are developments that impact less than 25 square metres (e.g. 5m by 5m) of habitat, or less than 5 metres of linear habitats, such as hedgerows
- householder applications
- development granted planning permission by a development order. This includes Permitted Development Rights
- biodiversity gain sites
- small scale self-build, and custom housebuilding
If the area of a site being impacted has a biodiversity unit value of zero, then BNG will not apply. Visit the government guidance on exemptions for information on what constitutes an 'impact'.
BNG hierarchy and rules
The biodiversity gain hierarchy states that developers must:
1. Avoid and reduce impacts: This is the first and most crucial step, focusing on preventing the loss of high and medium-value on-site habitats. This includes careful site selection and sensitive design to avoid harming existing biodiversity.
2. On-site habitat enhancement: Where damage can't be avoided, developers should enhance existing habitats on the development site to improve their ecological value.
3. On-site habitat creation: If further enhancement isn't sufficient, new habitats are created on the development site itself.
4. Registered off-site biodiversity gains: If on-site solutions aren't enough, developers can secure registered biodiversity units from off-site locations.
5. Statutory biodiversity credits: As a final resort, if none of the above options are available or sufficient, developers must purchase statutory biodiversity credits from the National Biodiversity Register.
Biodiversity metric rules
The following biodiversity metric rules must be followed, or biodiversity net gain cannot be claimed.
| Rule | Rule detail |
|---|---|
| Rule 1 | The trading rules of this biodiversity metric must be followed. |
| Rule 2 | Biodiversity unit outputs, for each type of unit, must not be summed, traded, or converted between types. The requirement to deliver at least a 10% net gain applies to each type of unit. |
| Rule 3 |
To accurately apply the biodiversity metric formula, the statutory biodiversity metric calculation tool or small sites biodiversity metric tool (SSM) for small sites must be used. The tools remove the need for a user to manually calculate the change in biodiversity value. The tool will summarise the results of the calculation and inform a user whether the biodiversity net gain objective has been met. |
| Rule 4 | In exceptional ecological circumstances, deviation from this biodiversity metric methodology may be permitted by the relevant planning authority. |
How BNG is calculated and assessed
BNG is calculated using the statutory biodiversity metric, which measures the biodiversity value of habitats in 'biodiversity units' as a proxy for nature. The biodiversity metric is used to assess how a development might change the biodiversity value of a site.
The metric subdivides the baseline assessment into three different unit modules based on habitat type. These can be 'habitat', 'hedgerow' or 'watercourse' unit modules. The metric then uses the changes in distinctiveness, extent, condition, and strategic significance to compare the biodiversity value of the proposed post-development habitats with the baseline, to determine if there is a net gain in biodiversity. When adopted, the West Sussex Local Nature Recovery Strategy (LNRS) should be taken into account when assigning strategic significance to habitats.
A small development may be eligible to use the simpler small sites metric statutory biodiversity metric (SSM) as part of the application. However, it should be noted that, for most developments, the application of BNG will require ecological expertise to interpret the inputs and outputs of the metric. The outputs can then help to inform the design, layout and management of a site to support biodiversity.
Biodiversity information that needs to be provided with a planning application
Both the national and local planning validation lists have been updated to respond to BNG requirements.
The national planning validation list requires major development to provide a fully completed statutory biodiversity metric calculation tool and supporting biodiversity net gain information.
The local planning validation list requires all development to provide a biodiversity net gain statement in accordance with Arun Local Plan Policy ENV DM5.
These biodiversity net gain requirements are in addition to the need to provide protected species and site surveys where applicable. Details of when these are required are also contained in the planning validation requirements [pdf] 665KB
The following information will be required:
- habitat report and maps
- Habitat condition assessment sheets and proven competency of ecologist, where appropriate
- statutory biodiversity metric in original Microsoft Excel and PDF format
- BNG statement
- Habitat Management and Monitoring Plan (HMMP) in draft following CIEEM good practice guidance, where appropriate
The BNG Statement should include:
i) Information about how adverse impacts on biodiversity have been avoided and minimised in accordance with the mitigation hierarchy
ii) Pre-development biodiversity value on-site habitat
iii) Post-development biodiversity value on-site habitat
iv) The proposed approach to enhance biodiversity on-site (including maps)
v) Any off-site BNG plans, including baseline and post-intervention biodiversity values, and maps.
A draft biodiversity gain plan may be submitted at the validation stage to provide information on how BNG is to be delivered and secured. A finalised biodiversity gain plan, alongside GIS shape files and final HMMP and biodiversity metric (where appropriate), must be submitted and approved before the commencement of the development. Any bespoke off-site land for BNG (see below) will need to be registered on the biodiversity gain site register via a legal agreement and allocated to the planning permission before the biodiversity gain plan can be approved.
For phased development, an overall biodiversity gain plan detailing the baseline and post-development interventions across the whole development must be submitted in as much detail as possible, to give certainty that BNG can be delivered long-term. A phased biodiversity gain plan for each phase detailing the contribution to the overall BNG will also need to be submitted and approved by the district council before development of that phase can begin.
Where BNG should be delivered
Biodiversity net gain can be delivered on-site, off-site or through a combination of on-site and off‑site measures following the biodiversity gain hierarchy which is where the impact on biodiversity should first be avoided, then minimised, then compensated as a last resort.
It is expected that the implementation of BNG should align with the local objectives and priorities for biodiversity improvements and nature recovery.
Off-site BNG (below) should ideally be located in Arun and as close to the development site as possible so that local communities benefit from enhanced biodiversity and nature is given an opportunity to recover. All off-site BNG land will need to be formally registered on the Natural England Biodiversity Gain Site Register.
As a last resort, applicants can purchase credits from the statutory biodiversity credit scheme, which go towards habitat creation plans across the UK. However, this will need to be approved by Arun District Council before purchase, and applicants will need to justify how they have rigorously followed the BNG principles and rules.
Habitat banks (off-site provision of BNG)
Identifying land as a habitat bank for off-site biodiversity net gain provides an opportunity to enhance land for nature and provide an income stream to the landowner to help manage the land for biodiversity.
A habitat bank is a gain site which is not linked to a particular development and usually provides biodiversity units for more than one development. The land will need to be registered as a biodiversity gain site using the government's online service.
Land provided for habitat banks will need to be legally secured for this purpose for a minimum of 30 years. A planning obligation (by way of a section 106 legal agreement) with the local planning authority or a conservation covenant with a responsible body will need to be used to secure the land.
BNG and significance
Paragraph 9 of Schedule 7A of the Town and Country Planning Act 1990 requires that any significant on-site habitat enhancement delivered as part of BNG, shall be secured for a minimum of 30 years. This can be secured by either a planning condition, an obligation in a legal agreement under Section 106 of the Town & Country Planning Act 1990, or a conservation covenant agreement. A BNG monitoring fee and the appropriate legal fee for drawing up the agreement will need to be paid.
BNG unilateral undertaking
In some instances, a unilateral undertaking can be used for minor and occasionally major applications, providing less than 0.5 units of medium distinctiveness habitat or hedgerow or more than 2 units of low distinctiveness habitat or hedgerow. The monitoring is based on reporting in years 1, 3 & 25 will attract the small site/low complexity BNG monitoring fee and legal fee. The unilateral undertaking template can be downloaded and completed by the applicant without the need for legal agreement: P32 - S106 UU BNG Template.docx [docx] 55KB
In some instances, it may be appropriate to consider the option to purchase credits if less than 0.25 units are required to achieve 10% BNG net gain.
Please see this guide for planning officers and applicants [pdf] 266KB on how significant on-site enhancements are viewed and how it is intended to secure this from new developments.
Please also visit our information for applicants on discharging the statutory gain plan condition.
Monitoring of BNG
BNG, secured through a section 106 agreement, will be monitored by the council and enforced if necessary. Failure to comply with the general biodiversity gain condition by commencing development without approval of the biodiversity gain plan will be a breach of planning control. The initial delivery and ongoing management of BNG will also be monitored and enforced if necessary.
Habitats created and enhanced under BNG must be monitored for a 30-year period. It is the responsibility of the applicant to carry out the monitoring of BNG and to submit reports to Arun District Council at agreed regular intervals across the stipulated management and monitoring period. The reports are due in years 2, 3, and 5 after the habitat works are completed and every 5 years thereafter up to the end of the 30-year agreement. Arun District Council will review and verify the reports and request that remedial action be taken where necessary.
The reports should contain: the BNG targets; an updated habitat survey and condition assessments; an updated statutory biodiversity metric showing the current biodiversity value of habitats; details of progress and further action towards achieving target conditions and any changes in the habitats since the latest monitoring report; recommendations for changes to the biodiversity gain plan as appropriate, and updated GIS shapefiles where necessary.
To cover the costs of the monitoring work, the council will charge a one-off up-front monitoring fee through a section 106 planning obligation. The fees vary depending on the size of the site and the distinctiveness of the habitats created or enhanced.
Further guidance from external websites
Understanding biodiversity net gain - gov.uk
Meet biodiversity net gain requirements: steps for developers - gov.uk