Biodiversity Net Gain (BNG)

There are some types of exempted development, and certain types of permission where the legal BNG requirement does not currently apply:

• Any planning applications for major developments made before 12 February 2024, or for minor developments made before 2 April 2024
• Householder applications as defined within article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015
• Developments where the site area is 0.2 hectares or less, unless onsite priority habitat is negatively impacted (applies to applications submitted from 6 August 2026)
• ‘De minimis’ development that does not impact a priority habitat, and impacts less than:
  
  
• 25 square metres onsite habitat
• 5 metres of onsite hedgerow or watercourse
  
  
• Temporary developments that do not impact onsite priority habitat and meet one of the following:
  
  
• The whole development is temporary
• Planning permission is granted for 5 years or less
  
  
• Developments solely or mainly for the creation of offsite BNG gains
• Urgent crown developments
• Developments granted permission by a development order (including permitted development rights)

Other types of permission that are not subject to the BNG requirement include:

• Reserved matters approvals (these are not applications for permission, the BNG requirement is attached to the original outline permission)
• Variations to planning permissions (section 73 applications) where the original application or permission was not subject to mandatory BNG
• Retrospective planning permissions made under section 73A
• Permissions in principle (but the subsequent technical details consent would be subject to the general biodiversity gain condition)

Please note that, even where one of the above exemptions may be met, development is still expected to ensure no net loss for biodiversity and where possible provide a net gain under local plan policy EM4.

Development delivering BNG will need to ensure certain statutory requirements are met, including:

• A minimum 10% BNG is achieved
• BNG is calculated using the latest version of the statutory biodiversity metric (or the ‘small sites metric’ for qualifying minor development)
• Adherence to the biodiversity gain hierarchy
• Secure, manage and monitor all offsite and significant onsite habitat enhancements for a minimum of 30 years

Development cannot commence until a Biodiversity Gain Plan (and relevant supporting information) is submitted to and approved by the local planning authority to discharge the pre-commencement condition.

Developers should refer to the planning practice guidance and government BNG statutory guidance for further detail on all statutory requirements.

Phased development

Specific BNG arrangements apply for development that is phased, to reflect the long-term timeframe. This includes an alternative approach to Biodiversity Gain Plans (BGP), where the outline permission will require the submission and approval of an Outline BGP, and subsequent reserved matters for each phase will require the submission and approval of a Phase BGP before commencement. Please refer to government guidance for further information.

Biodiversity gain hierarchy

In line with government guidance, developments must ensure they prioritise the delivery of BNG onsite first, and where it is not possible to deliver all of it onsite, then to secure offsite BNG. Where this is not possible, developers can purchase ‘statutory credits’ from the government as a last resort. These steps can be combined but must be followed in order.

It should be noted that the biodiversity gain hierarchy is distinct from the general mitigation hierarchy outlined in national policy, which should be considered as a first rule regarding the protection of biodiversity, i.e. avoid impacts in the first instance, where this is not possible mitigate those impacts, and as a last resort, compensate those impacts.

Small sites

Small sites (i.e. ‘minor’ development) may use the simpler ‘small sites metric’ provided no onsite priority habitat is being impacted and all BNG will be delivered onsite. For cases intending to deliver or secure offsite BNG, the full statutory metric should be used.

The biodiversity gain hierarchy is relaxed for small sites which means they can seek offsite BNG in the first instance if they wish.

Securing significant onsite BNG

The council has an established approach that any onsite BNG deemed as ‘significant’ must be legally secured via S106 agreement with the council as a long term and robust mechanism to ensure its implementation, management and monitoring over 30 years.

What constitutes significant onsite enhancements will be determined by the council on a case-by-case basis, but examples may include the creation of a wildflower meadow, a nature park, or a stretch of species-rich native hedgerow. A rough guide to what the council is likely to consider as ‘significant’ onsite enhancements includes:

• habitats of medium or higher distinctiveness
• habitats of low distinctiveness which create a large number of biodiversity units
• areas of habitat creation or enhancement which are significant in area relative to the size of the development

Significant onsite BNG will need to be delivered and monitored in line with a Habitat Management and Monitoring Plan, to be submitted and approved as part of the discharge of the biodiversity gain condition.

Habitat enhancements that are considered ‘non-significant’ may still require a planning condition to secure their implementation and management as considered necessary by the council.

Securing offsite BNG

All offsite BNG (i.e. BNG delivered on land outside of the red line boundary) must be secured by a legal agreement, either via a S106 with the council, or a conservation covenant with a Responsible Body. Developers can achieve this via one of the following ways:

• Developer-led offsite BNG on their own land – in this case the developer also acts as landowner. The following steps would need to be followed prior to submission of the Biodiversity Gain Plan to discharge the biodiversity gain condition:
• Obtain a legal agreement to secure the implementation, management and monitoring of the offsite BNG
• Obtain an approved Habitat Management and monitoring Plan (HMMP) and finalised metric (from the council in the case of a S106 agreement)
• Apply to register the site on the national Biodiversity Gain Site Register, ensuring submission of all required documentation (including plans, the legal agreement, full metric, HMMP, and a local land charge search certificate)
• Once registered, record the allocation of units to the development and obtain the necessary reference number from the Register to inform the Biodiversity Gain Plan.

Currently the council ensures the above steps are covered as obligations within the legal agreement issued alongside planning consent. The developer should ensure they factor in the time needed to complete these steps prior to development commencing. Please see government guidance for further advice for land managers.

• Purchase biodiversity units from the offsite BNG market – biodiversity units allocated under an established habitat bank scheme are already covered by the habitat bank’s own legal agreement and HMMP. The developer would need to have the allocation recorded to their development on the national Biodiversity Gain Site Register and provide evidence of this along with a fully completed statutory metric, to support its Biodiversity Gain Plan when applying to discharge the general gain condition before development commences.

Further information can be found here: Make off-site biodiversity gains as a developer - GOV.UK

Strategic significance

Strategic significance is the local significance of a habitat based on its location and habitat type. In Hampshire, the Hampshire Local Nature Recovery Strategy should be used to determine strategic significance. It can be applied in the metric for proposed habitats that fall within the Local Habitat Map and align with identified potential measures for that habitat parcel. This provides an enhanced ‘score’ so that more biodiversity units are generated (a 15% uplift), to incentivise developers to target BNG in mapped LNRS areas.

Please refer to the Statutory Metric User Guidance for further information.

Applications should be supported by information to enable the Council to make a full consideration as to whether the general condition is capable of being successfully discharged. For developments subject to BNG, the Planning Practice Guidance stipulates a statutory minimum level of information, set out below:

• a statement as to whether the applicant believes that planning permission, if granted, would be subject to the biodiversity gain condition
• the pre-development biodiversity value of the onsite habitat on the date of application (or an earlier date) including the completed metric calculation tool used showing the calculations, the publication date and version of the biodiversity metric used to calculate that value
• where the applicant wishes to use an earlier date, 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 date of application (or an earlier date) because of the carrying on of activities (‘degradation’) in which case the value is to be taken as immediately before the carrying on of the activities, and if degradation has taken place supporting evidence of this
• a description of any irreplaceable habitat (as set out in column 1 of the Schedule to the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations [2024]) on the land to which the application relates, that exists on the date of application, (or an earlier date)
• a plan, drawn to an identified scale which must show the direction of North, showing onsite habitat existing on the date of application (or an earlier date), including any irreplaceable habitat

In line with Planning Practice Guidance, the council may request further information at determination stage where necessary to help assist the council in its assessment of BNG proposals in light of existing local policy requirements, and to provide confidence that the BNG objective can be satisfactorily discharged.

The council encourages applicants to engage with its pre-application service to ensure any potential issues are identified, understood and resolved early on in the process, to reduce any future delay and improve the quality of a proposal.

For phased development the approach is slightly different. The outline application should be supported by a certain level of information to enable the council to make a full consideration as to whether the general condition is capable of being successfully discharged. This should include:

• The proposed balance between onsite and offsite gains
• Proposals for any significant onsite enhancements and how their implementation will be phased; and
• Information to inform a s106 legal agreement for both onsite and offsite gains.

This will usually mean the outline application should be accompanied by a full metric, pre and post development plans, and a draft Overall Biodiversity Gain Plan to provide the necessary information required.

Once planning permission is obtained, the developer will need to submit full BNG information to enable the discharge of the general gain condition, before the development can commence. This should include:

• Biodiversity Gain Plan – to include details of all offsite and significant onsite BNG provisions, the persons responsible for implementing the BGP, and biodiversity units as shown in the supporting metric. To ensure all the necessary information is provided, we recommend the use of DEFRA's Biodiversity gain plan template
• Fully completed metric tool
• Pre and post-development plans
• Biodiversity net gain register references for any offsite biodiversity units (where applicable)
• Proof of purchase for any statutory credits (where applicable)
• Habitat Management and Monitoring Plan for any significant onsite BNG and offsite BNG (where delivered by the developer) - to include responsibilities, a monitoring and reporting framework and a process for any remedial action needed. We recommend use of Natural England's HMMP template.

For phased development, please follow government guidance on what the Overall BGP and the Phase BGPs should include or be supported by.