Meeting Your BNG Requirements

The essence of BNG is to ensure that development doesn’t just seek to prevent or mitigate against biodiversity loss, but rather actively contributes to the enhancement of biodiversity and achieve measurably better outcomes for nature. 

The incorporation of BNG into the planning process, elevates the importance of biodiversity within the planning framework. It requires a more holistic approach to development that sets an expectation for developers to consider biodiversity from the outset as an essential component of a scheme and to make conscious decisions to deliver more or better-quality natural habitat than there was before. 

Calculating Biodiversity Value

Habitat value is measured using either Natural England’s Statutory Biodiversity Metric or the Small Sites Metric (SSM). 

• The Statutory Biodiversity Metric must always be used for development which meets the definition of ‘major development’, or where the criteria to allow the use of the SSM have not been met.
• The Small Sites Metric is a simplified version of the Statutory Biodiversity Metric and can be used for development which meets the definition of ‘small sites’, and where the criteria to allow the use of the SSM are met. The Statutory Biodiversity Metric can always be used in its place.

The metric tools are effectively a calculator for biodiversity and work by assigning a unit value to habitats present within the development’s red line boundary, according on their importance, condition and distinctiveness. The metric determines the net biodiversity gain of a development proposal by accounting for the difference between the habitat loss resultant from the development footprint and the habitats created and/or enhanced through the landscaping strategy.

In circumstances where development activities have been carried out on site prior to the submission of a planning application and are not in accordance with a planning permission, then the pre-development biodiversity value of the site will be taken to be its biodiversity value immediately before these activities were undertaken.

The Statutory Biodiversity Metric and the SSM should be completed in accordance with the biodiversity metric rules and principles set out in the Statutory Biodiversity Metric User Guide or the Small Sites Metric User Guide. Links to these can be found on the Validation, Guidance and Tools page.

The Biodiversity Gain Hierarchy

The Biodiversity Gain Hierarchy is distinct from, but complementary to, the Mitigation Hierarchy that is enshrined in paragraph 186a of the National Planning Policy Framework. 

Biodiversity net gain should be achieved in a way that is consistent with the mitigation hierarchy, and which reflects the spatial hierarchy preference for local enhancements. Whilst biodiversity net gain relates only to habitats, the mitigation hierarchy is applied to all aspects of ecology and potential for avoidance, minimisation, mitigation and offsetting impacts on species will also need to be considered outside of a BNG approach. 

The Biodiversity Gain Hierarchy outlines the steps developers should follow in order of priority when planning and implementing biodiversity improvements for their projects. 

1. Avoiding Adverse Effects: Adverse effects on existing on-site habitats should be avoided entirely or minimised. In particular habitats with a medium or higher distinctiveness score (four or more on the biodiversity metric). 
2. Mitigate Unavoidable Effects: In so far as those adverse effects cannot be avoided, mitigating those effects.
3. Enhance On-Site Habitats: In so far as those adverse effects cannot be mitigated, habitat enhancement of on-site habitats.
4. Create New On-Site Habitats: In so far as there cannot be that enhancement, creation of on-site habitats.
5. Secure Off-Site Biodiversity Units: In so far as there cannot be that creation, the availability of registered off-site biodiversity gain.
6. Purchase Biodiversity Credits: In so far as that off-site habitat enhancement cannot be secured, purchasing biodiversity credits.
    

Developers are encouraged to follow the biodiversity gain hierarchy from the outset of a project; and must be prepared to demonstrate how their chosen approach to meeting the BNG requirement has adhered to the biodiversity gain hierarchy and achieves the best outcomes for nature. 

Ways of Meeting the BNG Requirement

In addition to the biodiversity mitigation hierarchy, planning practice guidance sets out a sequential hierarchy of BNG delivery.

1. On-site: The creation and/or enhancement of habitats on-site is the preferred option for the delivery of the biodiversity gain. This ensures that ecological connectivity and value is kept within close proximity to habitats that are being lost and local communities’ benefit from increased access to, or views of, nature.

2. Off-site: Where on-site opportunities are not possible or have been exhausted, developers can look to meet all or part of their BNG requirements on land that they own elsewhere. Habitats that are either enhanced or created off-site must be secured by legal agreement such as a S106 or a conservation covenant; and registered with Natural England. Alternatively, the number of biodiversity units needed to meet net gain requirements can be purchased from a registered habitat bank.

3. Purchase of Biodiversity Units or Credits: Where unable to satisfy BNG on-site, off-site, or  through the purchase of biodiversity units, developers can, with the prior permission of the Council, purchase statutory credits from the Government. 

Strategic Significance

'Strategic significance’ is an important part of the biodiversity metric scoring approach. The ‘strategic significance’ score is a landscape scale factor, which gives additional biodiversity unit value to habitats that are located in preferred locations for biodiversity and other environmental objectives.

On 27 November 2025, Kent County Council published the Kent and Medway Local Nature Recovery Strategy (LNRS), which should now be used to determine the 'strategic significance' multiplier when completing the biodiversity metric.

Spatial Risk Multiplier

The Spatial Risk Multiplier aligns with the Biodiversity Gain Hierarchy and is about recreating lost habitats as close to the development site as possible, to ensure ecosystem continuity, preserve genetic diversity, and to provide direct benefits for local wildlife and communities.

The spatial risk multiplier is another critical element of the biodiversity metric, that incentivises local nature recover by imposing unit penalties on developers the further the biodiversity units being created or purchased from the original development site. 

For biodiversity units being created or purchased:

• In the same local planning authority (LPA) area or the National Character Area (NCA) to where the development occurs, the multiplier applied is 1 (i.e. no penalty).
• In a neighbouring LPA or NCA to where the development occurs, the multiplier applied is 1.5x (i.e. 50% more).
• In another part of England, the multiplier applied is 2x (i.e. 100% more).  

Purchasing Biodiversity Units or Statutory Credits

Qualifying developments are now required to deliver a minimum 10% biodiversity net gain. Wherever possible this should be met through on-site habitat enhancements and/or creation.  

Where this is not possible and can be demonstrated through the application of the biodiversity gain hierarchy, developers can choose to either meet their requirements off-site on land that they own elsewhere or purchase biodiversity units from a registered habitat bank. If neither of these are options are available, or the required number of biodiversity units is 0.25 or less, then statutory credits can be bought from the Government with the prior approval of the Council. 

Evidence that the correct number of units or credits have been purchased to meet the BNG requirement must be submitted as part of the Biodiversity Gain Plan to discharge the statutory condition.

Biodiversity Units

The purchasing of biodiversity units is a 'free market', with the price agreed between the developer and the habitat bank owner. There is no national or local set price for biodiversity units, and Ashford Borough Council are not able to advise or support brokering any such negotiations or purchases.

The purchasing of biodiversity units can be quite complicated, as such we’d always advise that developers consider seeking specialist help, to ensure that the right quantity, and type of units are bought to meet your BNG requirement.

The Biodiversity Net Gain (BNG) Site Register for Kent and Medway can be used to help find available and/or prospective biodiversity units for sale. View the Kent biodiversity Net Gain Site Register.

Statutory Credits 

In circumstances where it can be evidenced that the quantity and/or type of biodiversity units required are not available to purchase from a private habitat bank, or where the number of biodiversity units required is less the 0.25, then developers have as a last resort, the option to buy statutory biodiversity credits from the Government, with the prior approval of the Council. View the statutory biodiversity credits webpage. 

These credits fund government-led or approved conservation and habitat creation projects elsewhere, thus contributing to national biodiversity goals. However, given that these are disconnected from the site where the development has taken place, and where the ecosystem has been damaged, the spatial risk multiplier applies. 

The prices of Biodiversity Credits are advertised online and based on the value of different habitats. Unlike most private suppliers, credits can be bought in fractions up to two decimal places, or 0.01 credit.

Securing BNG

Any significant on-site biodiversity gains; and all off-site biodiversity gains must be secured by a S106 legal agreement for at least 30 years; and accompanied with a Habitat Management and Monitoring Plan.