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.  

Paragraph 174 of the National Planning Policy Framework (NPPF, 2021) requires biodiversity net gains to be achieved and the Government has made it a mandatory requirement for certain development to achieve a minimum 10% BNG through the Environment Act 2021. It is currently anticipated that mandatory BNG will be required from Autumn 2023; secondary legislation and guidance will be published to support implementation.  

Purpose of this interim Technical Advice Note

The purpose of this Technical Advice Note (TAN) is to provide interim guidance for planning applicants and decision makers on how BNG will be achieved in Brighton & Hove in accordance with the policy requirements of City Plan Parts 1 and 2, prior to BNG becoming a mandatory requirement. 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 provides guidance on BNG. 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 prior to the provision of any BNG.   

Local policy requirements 

The key local planning policies which require BNG are City Plan Part 1 Policy CP10 Biodiversity; and 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.  

Biodiversity Net Gain requirements

When will BNG be required in Brighton & Hove? 

The council is phasing the implementation of requirements for measurable BNG. Initially, only major planning applications submitted after the adoption of City Plan Part 2, 20th October 2022 will be required to provide measurable BNG.  

It is currently anticipated that minor applications will be required to provide measurable BNG from Autumn 2023. This TAN will be updated and reviewed as necessary.   

How much BNG is required? 

A minimum 10% BNG is sought reflecting the forthcoming 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 interim BNG requirements expected for various types and scales of development and shows how this should be measured. The second list sets out the interim exemptions from BNG. 

NB: This interim TAN sets out BNG requirements for development ahead of mandatory BNG. Forthcoming regulations will specifically identify the types of development that are exempt from providing BNG when it becomes a mandatory requirement. 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.  

Interim BNG requirements 

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 

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 

Interim exemptions from measurable BNG 

Type of development  

  • Minor development 

  • Householder development 

  • Permitted development 

  • Prior approvals 

  • Change of use 

Interim requirements 

Measurable BNG not currently required. 

Proposals should still include application of the mitigation hierarchy and appropriate measures that support the enhancement of biodiversity. For example, bee bricks, swifts 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 prior to development and proposed through development. This allows the pre and post development biodiversity value to be calculated by an ecologist. 

Biodiversity Metric (currently version 3.1) 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 in accordance with 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 consultation confirms that BNG should be achieved in a way that is consistent with the mitigation hierarchy. BNG should therefore be provided on-site in the first instance and be designed appropriately for the development and local situation. Government guidance is expected to clarify options for what BNG will look like for urban sites or those sites with a very low baseline. Ahead of mandatory requirements, the priority in Brighton & Hove will be for onsite BNG.  

What if BNG can’t be achieved on site? 

Where it is 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). A LNRS for East Sussex and Brighton & Hove will be prepared in 2023-24. 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.  

Further details about off-site provision are expected through forthcoming regulations. 

What is required to support a planning application

All of the following information should be submitted with the planning application and will be required for validation purposes: 

  • Biodiversity Net Gain Report
    Forthcoming government regulations will provide further details on what should be included in a BNG Report. Prior to the publication of these regulations, a report in line with the Biodiversity Net Gain Report and Audit Template (CIEEM, 2021) should be submitted for full or reserved matters applications. The BNG Report should include: 

    • Information about how adverse effects have been avoided and minimised in accordance with the mitigation hierarchy 
    • Pre-development biodiversity value of on-site habitat 
    • Post-development biodiversity value of on-site habitat 
    • Proposed approach to enhancing biodiversity on site 
    • Any off-site BNG proposed and its value 
  • The completed relevant full Biodiversity Metric in excel and pdf format. A summary is not acceptable.  
  • A biodiversity baseline assessment/ecological study which meets the requirements of the relevant Biodiversity Metric used.  
  • Habitats plan, showing habitat lost, enhanced and created. This should clearly show where the habitat units occur for both pre-development (baseline) and post-development values.  

Prior to the commencement of development, information about how the habitat enhancement and/or creation will be implemented, managed and monitored for a minimum of 30 years must be provided. This should be provided in a BNG Implementation, Management and Monitoring Plan which follows good practice guidance. Alternatively, this information could be incorporated within a Landscape and Ecology Management Plan (LEMP) where this is required.  

Requirements for outline and reserved matters applications 

For outline applications, it will be necessary to demonstrate that the development can achieve BNG in principle. Initial versions of the documents outlined in (a) to (d) above will be required based on information available at the time. This includes an initial run of the Biodiversity Metric, a proposed habitats plan based on an indicative layout plan and a Biodiversity Net Gain Feasibility Assessment report (CIEEM, 2021). An up-to-date habitat survey will still be needed to establish the baseline for the site. An indication of the post-development value using the Biodiversity Metric should be provided based on the proposed habitats plan.   

Reserved Matters applications should continue to demonstrate that BNG will be achieved and should add more detail to the Biodiversity Gain Report, Biodiversity Metric and other required evidence as appropriate, based on finalised layout plans.  

Where a development is to be phased, a biodiversity net gain strategy must be submitted at the outline stage, which shows how individual phases deliver a predetermined proportion of the biodiversity value. Reserved matters applications will then be required to demonstrate exactly how each phase will meet its biodiversity requirements with the majority of BNG provided in the first phases of development. 

How to complete a Biodiversity Metric

Natural England have produced a comprehensive user guide for completing the Biodiversity Metric 3.1 which should be referred to. Key points include: 

  • The Metric must be completed by a suitably qualified and experienced ecologist. 

  • Baseline habitat surveys must be undertaken during the appropriate survey season to inform completion of the metric.  

  • Habitat surveys must include an assessment of their condition and distinctiveness. 

  • The UKHab is the default format for habitat surveying for the metric.  

Strategic Significance 

The 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.  

Prior to the production and adoption of a Local Nature Recovery Strategy, the following are considered of strategic significance in Brighton & Hove:  

  • Special Areas of Conservation 

  • Sites of Special Scientific Interest 

  • Local Nature Reserves 

  • Local Wildlife Sites 

  • Biodiversity Opportunity Areas 

Which types of biodiversity enhancement count as measurable BNG

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 and mixed scrub.  

The 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 and 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

Management and monitoring

BNG will be required to be managed and monitored for a period of 30 years. 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 is envisaged that typically reports will be required for years 2, 5, 10, 20 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 BNG Report.   

Future provisions for management and monitoring for mandatory BNG will be set out in forthcoming government regulations.   

Securing BNG

The implementation and ongoing monitoring of on-site BNG will be secured through planning conditions.  

It is envisaged that the implementation and monitoring of off-site BNG will be secured through a conservation covenant. This 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.