1 Overview
Biodiversity net gain (BNG) is a government initiative. It ensures that after development the habitat for wildlife is measurably better than it was before. BNG became a mandatory requirement in the planning system for:
- major development from 12 February 2024
- minor development from 2 April 2024
The developer must measure the site’s biodiversity before development. They must provide a 10% increase in the biodiversity measurement as part of the development. This can be delivered:
- on-site
- off-site
- through a combination of on-site and off-site
The provision, management and monitoring of significant BNG must be legally secured for a minimum of 30 years.
The need for BNG does not change other requirements and protections for the natural environment, such as designated nature conservation sites and important habitats and species.
The county council offers a pre-application advice service. Developers can use this to receive informal advice from officers about meeting the BNG requirement.
2 Exemptions
If a site has no biodiversity it is given a unit value of zero and BNG will not apply.
The government decide the criteria for exemption. The relevant exemptions for planning applications West Sussex County Council determine are:
- retrospective planning permissions - made under section 73A of the Town and County Planning Act 1990
- variation of condition permissions made under section 73 where the original permission was either
- granted before mandatory BNG
- the application for the original permission was made before mandatory BNG
- planning permission granted by a development order under Section 59, including permitted development
- development subject to the de minimis exemption – that does not impact a priority habitat which is either:
- less than 25 square metres (5m by 5m) of habitat
- 5 metres of linear habitats, such as hedgerows and watercourses
- development of a biodiversity gain site – undertaken solely or mainly for the purpose of fulfilling, in whole or in part, the biodiversity gain planning condition, which applies in relation to another development
- review of old mineral permissions (ROMP) made under the Environment Act 1995
Developments that are exempt from mandatory BNG should still minimise impacts on and provide net gains for biodiversity. In accordance with the National Planning Policy Framework (NPPF). They can do this by:
- establishing coherent ecological networks that are more resilient to current and future pressures
- incorporating features that support priority or threatened species
3 Measuring
BNG is calculated using the statutory biodiversity metric. This measures the value of habitats in ‘biodiversity units’.
The metric compares the:
- baseline score for the site's pre-development
- score for the proposed post-development habitats
To determine if there is a net gain in biodiversity, the metric uses changes in:
- distinctiveness
- extent
- condition
- strategic significance
You must not undertake pre-emptive site clearance to reduce the biodiversity value of a development site prior to a baseline assessment.
The metric can help to inform changes to the design, layout, and management of a site to support biodiversity. It assesses how development may change a site's biodiversity value.
Assessing the biodiversity metric requires ecological expertise.
The assessment will need to take account of how much of the various habitats on the site you will retain, enhance, or lose as a result of the proposed development.
It also takes into account habitat creation and enhancement plans and follows the principle of equivalence - replacing with like-for-like or better habitats.
For more information, view GOV.UK pages about the biodiversity metric.
Other requirements and protections
BNG must be additional to any mitigation or compensation measures for protected species.
This means at least 10% of the overall net gain via habitat creation and enhancement must be additional to any existing obligations.
4 Strategic significance
There are 3 categories of strategic significance:
- high - information on the habitat type is mapped and described as locally ecologically important within a specific location
- medium - a site that is considered ecologically desirable but not in a local strategy
- low - all other habitats.
You must explain the justifications for assigning high or medium strategic significance to a habitat in the the metric. Use the ‘user comments’ column for this.
The West Sussex Local Nature Recovery Strategy (LNRS) will identify the habitats of strategic significance where off-site BNG would best be delivered; this approach is incentivised by the biodiversity metric.
In advance of approval of the LNRS, scheduled for winter 2025-2026, alternative documents should be used for assigning high, medium and low strategic significance levels, including but not limited to:
- Draft Local Nature Recovery Strategy
- Local Plans and Neighbourhood Plans
- Local Planning Authority Ecological Networks
- Tree Strategies and Woodland Strategies
- National Landscape Management Plans
- Biodiversity Action Plans
- Species conservation and protected sites strategies
- Green Infrastructure Strategies
- River Basin Management Plans
- Catchment Plans and Catchment Planning System
Relevant information is available on the District and Brough Council’s websites and should be considered when assigning strategic significance to habitats. Further information is available on Table 8 of the biodiversity metric user guide and the meaning of each level of strategic significance is set out above.
5 Delivering
You should plan your actions for adverse impacts on biodiversity using the mitigation hierarchy. This specifies the order as:
- firstly, avoided
- secondly, mitigated
- thirdly, compensated for on-site
- finally, compensated for off-site
You should achieve BNG on-site where possible and ecologically suitable. This should be a key consideration when designing development proposals.
You should deliver any off-site BNG as close as possible to the development site. This provides benefits to local biodiversity and communities.
Where possible, you should direct any off-site BNG towards habitats of high and medium strategic significance.
You can purchase biodiversity units on the open market to deliver BNG at a ‘habitat bank’ that has been registered on the biodiversity gain site register.
Find further information on the GOV.UK section about making biodiversity gains as a developer.
6 Required information
You will need to support planning applications subject to the BNG requirement with the following information:
- BNG strategy statement with information about:
- how adverse impacts on biodiversity have been avoided or minimised
- pre-development value of on-site habitats
- post-development value of on-site habitats
- the proposed approach to enhance biodiversity on-site
- any off-site plans (including baseline and post-intervention biodiversity values)
- draft biodiversity metric - to include:
- habitat condition assessment sheets
- proven competency of the assessor
This is set out in the local list for the validation of planning applications.
Where appropriate, to inform discussions about feasibility, securing and monitoring of BNG, you should include a draft:
For phased development, to give certainty that BNG can be delivered long-term, you should include an:
- overall biodiversity gain plan, detailing the baseline and post-development interventions
7 Securing
The government requires the council to secure BNG when determining planning applications.
Once planning permission has been granted, you must submit a final biodiversity gain plan. You must receive our approval before you start your development.
The submission of a biodiversity gain plan is subject to a fee of £145 per application or request.
You will also need to submit, where appropriate, a plan for each individual phase. This should detail its contribution to overall BNG. You will need the county council's approval before you can begin each phase of development.
A legal agreement will secure the provision, management, and monitoring of significant on-site and all off-site BNG for a minimum of 30 years. The applicant must meet this cost. Find more information on GOV.UK.
What counts as ‘significant’ will depend on the existing habitats within the application site and the scale of the proposed development.
Before we can approve the biodiversity gain plan, you must register any off-site BNG secured by legal agreement on the biodiversity gain site register and allocate it to the planning permission.
8 Monitoring
The government requires the council to monitor its provision at regular intervals during the required management and monitoring period.
It is the applicant's responsibility to carry out the monitoring of BNG and submit reports to the council.
The reports should contain:
- the BNG targets
- updated habitat survey and condition assessments
- updated biodiversity metric showing the current biodiversity value of habitats
- details of progress towards achieving target conditions
- further action towards achieving target conditions
- any changes in the habitats since the last report
- if required, recommended changes to the biodiversity gain plan
The council will review and verify the reports, requesting remedial action where necessary.
We will secure the cost of monitoring and reporting over 30 years through legal agreements. The following fees apply:
- small site (0-10 hectares) - £4,155
- medium site (11-20 hectares) - £5,130
- large site (21 hectares) - £6,105
The fees include the costs of:
- set-up
- registration costs
- six site visits to take place in years 1, 5, 15, 25, 30 and 1 unscheduled visit
- reviewing the monitoring reports
We will review the monitoring plan and make adjustments as necessary.
Proposed fees include yearly inflation of 3% per annum. We will review fees as required.