Biodiversity Net Gain

What is Biodiversity Net Gain?

The idea behind Biodiversity Net Gain (BNG) is that development should leave biodiversity in a measurably better state than it was before any development took place.

BNG is defined as leaving more, bigger or better habitats for biodiversity and is demonstrated by using the DEFRA biodiversity metric. It's demonstrated by using the DEFRA Statutory Biodiversity Metric for major applications and the DEFRA Small Sites Metric for minor applications.   

Paragraph 180 of the National Planning Policy Framework (NPPF, 2023) requires biodiversity net gains to be achieved.

The Government has made it a mandatory requirement for certain development to achieve a minimum of 10% BNG through the Environment Act 2021.

Mandatory BNG is required for:

• major developments since 12 February 2024
• minor developments from 2 April 2024

Secondary legislation and guidance have been published to support implementation.  

Purpose of this Technical Advice Note

The purpose of this Technical Advice Note (TAN) is to guide planning applicants and decision-makers on how BNG will be achieved in Brighton & Hove to meet the mandatory requirement, as well as the policy requirements of City Plan Parts 1 and 2.

This TAN explains: 

• the type of development required to provide BNG
• the amount of BNG required
• how BNG should be measured
• the information required to be submitted with your planning application
• information on the types, locations and extent of habitats that can provide BNG
• how BNG will be secured
• how BNG will be monitored

This TAN only guides BNG.

Biodiversity and Nature Conservation SPD11

The council has produced an updated Biodiversity and Nature Conservation SPD11 to assist planning applicants to better understand the importance of biodiversity more generally and ensure they meet legislative and policy requirements.

The SPD provides a step-by-step guide for ensuring biodiversity is properly considered throughout the planning process.

The SPD should therefore be referred to for all other matters concerning biodiversity, including the overarching principles that apply to development, such as the mitigation hierarchy which must be addressed before the provision of any BNG.   

Local policy requirements 

The key local planning policies which require BNG are:

• City Plan Part 1 Policy CP10 Biodiversity
• City Plan Part 2 Policy DM37 Green Infrastructure and Nature Conservation

Both policies seek BNG from development, with DM37 requiring BNG to be measurable.

Section 4.2 of SPD11 provides more details on the local policy requirements relating to BNG and biodiversity.  

When will BNG be required in Brighton & Hove? 

The requirement to provide measurable BNG was implemented in Brighton & Hove ahead of the mandatory requirement. Initially, only major planning applications submitted after the adoption of City Plan Part 2 (20 October 2022) were required to provide measurable BNG.  

Minor applications will be required to provide measurable BNG from 2 April 2024. This is in line with the national implementation of BNG.

This TAN will be updated and reviewed as necessary.   

How much BNG is required? 

A minimum of 10% BNG is required, reflecting the requirements of the Environment Act.  

Net gains are additional to any mitigation or compensation that is required to address development impacts.

Development must therefore accord with the mitigation hierarchy and additionally achieve net gains for biodiversity. This is explained further in Section 5 of SPD11.  

What type and scale of development does BNG apply to? 

The following list sets out the BNG requirements for various types and scales of development and shows how this should be measured. 

The second list sets out the national exemptions from BNG. 

This TAN will be updated once the regulations are published.

BNG does not apply to any development where the on-site habitat includes irreplaceable habitats, as defined in the NPPF Annex 2, nor does it replace existing protections, for example for designated sites or protected species.

BNG requirements 

Major residential development 

• Scale
  • development is 10 or more dwellings; or 
  • The number of dwellings is not known and the site area is greater than 0.5 hectares. 
• Requirement 
  • Minimum 10% BNG; on-site opportunities maximised  
• Biodiversity Metric 
  • Statutory Biodiversity Metric

Minor residential development

• Scale
  • development of between 1-9 dwellings; or
  • the number of dwellings is not known and the site area is less than 0.5 hectares
• Requirement
  • (from 2 April 2024) minimum 10% BNG; on-site opportunities maximised
• Biodiversity Metric
  • Small Sites Metric (provided no priority habitat or European species are on site) 

Major non-residential development

• Scale
  • floorspace is 1,000m2 or more; or 
  • The amount of floorspace is not known and the site area is greater than 1 hectare. 
• Requirement 
  • Minimum 10% BNG; on-site opportunities maximised  
• Biodiversity Metric 
  • Statutory Biodiversity Metric

Minor non-residential development

• Scale
  • floorspace is less than 1,000m2; or 
  • the amount of floorspace is not known and the site area is less than 1 hectare
• Requirement 
  • (from 2 April 2024) Minimum 10% BNG; on-site opportunities maximised 
• Biodiversity Metric
  • Small Sites Metric (provided no priority habitat or European species are on site) 

The requirements for minor development apply to applications made after 2 April 2024. 

Exemptions from 10% BNG 

Type of development   

• householder development 
• permitted development 
• prior approvals 
• development that does not impact priority habitat and impacts less than 25sqm of habitat that has a biodiversity value greater than zero or 5m of linear habitat such as hedgerows
• self-build and custom-build development providing no more than 9 dwellings on a site no larger than 0.5 hectares
• sites developed to provide off-site BNG 

Proposals should still include the application of the mitigation hierarchy and appropriate measures that support the enhancement of biodiversity. For example:

• bee bricks
• swift bricks
• biodiverse landscaping

See SPD11 Section 6 for guidance.

How is BNG measured? 

BNG should be measured using the most recent version of the relevant Biodiversity Metric.

The Biodiversity Metric calculates a proxy biodiversity value based on the type and condition of habitats present on site before development and proposed through development. This allows the pre and post-development biodiversity value to be calculated by an ecologist.

View the Statutory Biodiversity Metric and user guide.

Further details on carrying out the BNG assessment can be found in Section 7 of SPD11.  

At what point in the planning process should BNG be considered? 

BNG needs to be considered at the very start of the design process with baseline habitat surveys informing the design following the mitigation hierarchy.

Further details on the mitigation hierarchy, BNG and when to consider BNG can be found in Sections 5 and 7 of SPD11.

Where should BNG be provided?  

Government guidance confirms that BNG should be achieved in a way that is consistent with the Biodiversity Gain hierarchy. This emphasises that onsite biodiversity gains should be considered first, followed by offsite biodiversity gains on registered sites, with biodiversity credits as a last resort. 

BNG should therefore be provided on-site in the first instance and be designed appropriately for the development and local situation.

The priority in Brighton & Hove will be for onsite BNG.  

What if BNG can’t be achieved on-site? 

Where it's clearly demonstrated that meaningful on-site BNG cannot be achieved, off-site opportunities should be pursued.

SPD11 indicates that off-site BNG could be provided for at ‘local strategic sites’, having regard to any emerging Local Nature Recovery Strategy (LNRS).

An LNRS for East Sussex and Brighton & Hove is in preparation with a target publication date of summer 2025. Before this, certain sites are regarded as having strategic significance, such as Local Wildlife Sites.

In the interim, the council is considering how it can provide a role in facilitating the provision of BNG in those instances where it cannot be delivered on-site.  

The following mandatory information must be submitted with the planning application and will be required for validation purposes. In addition, we require some additional information which should be submitted with the planning application.

Mandatory Validation Requirements

Validation requirements include:

• a statement indicating whether BNG is applicable or the reasons why not, where relevant 
• the completed Biodiversity Metric showing the pre-development biodiversity value of onsite habitat on the date of application (or earlier date) (to be submitted in Excel and PDF format)
• where an earlier date is proposed, the proposed earlier date and the reasons for proposing that date
• a statement confirming whether the biodiversity value of the onsite habitat is lower on the application date due to any degradation activities; 
• a description of any irreplaceable habitat on the site
• a scale plan showing onsite habitat on the date of application (or earlier date), including irreplaceable habitat 

Local Validation Requirements

A draft Biodiversity Gain Plan which sets out the following additional information:

• the approach to how adverse effects have been avoided and minimised
• the baseline habitat conditions survey
• the proposed post-development biodiversity value of on-site habitat, calculated using the Biodiversity Metric
• any off-site BNG proposed and its value
• a description of arrangements for habitat management and monitoring

Where on-site BNG is proposed: 

• a scale plan showing the proposals for habitat enhancement or creation required to meet post-development value 

Requirements for outline and reserved matters applications 

Outline applications are subject to the same provisions for BNG as described above.   

Reserved Matters applications should:

• continue to demonstrate how BNG will be achieved
• add more detail to the Biodiversity Metric and other required evidence as appropriate, based on finalised layout plans

Once planning permission has been granted and before the commencement of development, a finalised Biodiversity Gain Plan must be submitted and approved by the council.

The Biodiversity Gain Plan will be secured by condition.

The final Gain Plan must include:

• a statement which sets out steps taken to minimise adverse effects on biodiversity
• the completed biodiversity metric showing pre and post-development biodiversity value
• any registered off-site BNG units allocated to the development and their value
• any biodiversity credits purchased
• a description of arrangements for maintenance and monitoring habitat enhancements for a minimum of 30 years
• how the Biodiversity Gain Hierarchy will be followed
• pre-development and post-development plans, to scale, showing onsite habitat
• arrangements for compensation for any irreplaceable habitat, where relevant

There are also additional requirements including:

• the name and address of the person completing the plan
• the planning reference number
• a description of the development to which the plan relates

Requirements for Phased Development

A phased development is a development that has outline planning permission where the permission identifies clear phases for development, which would be subject to subsequent reserved matters approvals.

These requirements do not apply to outline and reserved matters applications where the development is not delivered in phases. 

Phased development must submit:

• an Overall Biodiversity Gain Plan before the commencement of any development
• a Phase Biodiversity Gain Plan for each phase before the commencement of that phase 

The Overall Biodiversity Gain Plan should set the framework for how the minimum 10% BNG is expected to be achieved across the entire development.

Each Phase Biodiversity Gain Plan should set out each phase’s contribution and track progress towards the overall biodiversity gain objective.

It's envisaged that the Phase Biodiversity Gain Plan would be submitted at the Reserved Matters stage for each phase. 

Further details of what each Biodiversity Gain Plan should include are set out in Government Guidance. 

Defra has produced a comprehensive user guide for completing the Statutory Biodiversity Metric. This includes 9 principles and 4 rules which must be followed.

Key points include: 

• the Biodiversity Metric must be completed by a suitably qualified and experienced ecologist
• the metric does not change existing protection or obligations, and good practice guidance and professional codes still apply
• habitat interventions must be deliverable and realistic
• biodiversity unit outputs for each type of unit (area/habitat, linear habitat and watercourse) cannot be summed, traded or converted between types

Strategic significance 

The Biodiversity Metric includes a section on strategic significance.

Strategic significance is whether the location of each habitat parcel is identified in a local plan or other strategic document as an important area for biodiversity.

Strategic documents for biodiversity often include planning documents such as supplementary planning documents and local plans, or within local nature recovery strategies, biodiversity opportunity areas and biodiversity action plans.  

Before the production and adoption of a Local Nature Recovery Strategy, the following are considered to be of high or medium strategic significance in Brighton & Hove:  

High significance:

• Special Areas of Conservation
• Sites of Special Scientific Interest
• Local Nature Reserves
• Local Wildlife Sites

Medium significance:

• Biodiversity Opportunity Areas

Biodiversity Opportunity Areas are shown in Section 4 of SPD11.

Within the Brighton & Hove Urban Green Network Biodiversity Opportunity Area (which is also the Nature Improvement Area (NIA)), any enhancements should meet the objectives of the NIA (see City Part 1 policy CP10 Biodiversity). 

Measurable BNG is based on enhancements to existing habitats or the creation of new habitats.

The Biodiversity Metric lists all the different types of habitats that can either be present within the application site, or that could be provided as measurable BNG.

This includes locally important habitats such as:

• lowland calcareous grassland
• broadleaved woodland
• mixed scrub

The Biodiversity Metric also lists a variety of habitats that are specifically found or could be provided as BNG within an urban context. This includes:

• allotments
• biodiverse green roofs
• green walls
• shrubs
• urban trees
• sustainable urban drainage features

Some of these habitats and measures may be more achievable for proposals situated within the built-up area of Brighton and Hove.  

All proposed measures should be appropriate to the development, site location and surroundings.  

Although species-based measures such as swift bricks do not count as measurable BNG, these types of measures are still important for biodiversity and should be provided where possible.  

Various examples of species and habitat-based measures that can help incorporate biodiversity into development can be found in Section 6 of SPD11. 

Significant on-site BNG, and all off-site BNG, will be required to be managed and monitored for a period of 30 years. 

Whether on-site habitat is considered to be significant will vary depending on the scale of development and existing habitat but would normally be:

• habitats of medium or higher distinctiveness in the Biodiversity Metric
• habitats of low distinctiveness which create a large number of biodiversity units relative to the value of the site before development
• habitat creation or enhancement where distinctiveness is increased relative to the distinctiveness of the habitat before development
• area of habitat creation which are significant in an area relative to the size of the development
• enhancements to habitat condition, for example from poor or moderate to good

Further local guidance may be produced to help identify whether habitat is considered significant. 

It will be the landowner or developer’s responsibility to ensure monitoring and reporting obligations are fulfilled.

Monitoring should be proportionate. The number of monitoring assessments will depend on the size of the proposal, and the habitat types and extent, but it's envisaged that typically reports will be required for years: 2, 5, 10, 15, 20, 25 and 30.

As a minimum, reports should include a summary of habitat type, extent and condition, with a comparison against the expected condition proposed within the submitted Biodiversity Net Gain Plan.

A Habitat Management & Monitoring Plan (HMMP) template is available for use. 

Onsite

The implementation of non-significant on-site BNG will be secured through planning conditions.

Off site

The implementation and monitoring of significant on-site and all off-site BNG will be secured through a Section 106 agreement or conservation covenant.

A conservation covenant is a legally binding agreement between a landowner and a designated “responsible body” to provide BNG on their land. 

It will be the developer’s responsibility to take out a conservation covenant. Forthcoming government regulations will set out provisions for the use of conservation covenants.