Biodiversity Net Gain
Biodiversity net gain (BNG) is an approach introduced under the Environment Act 2021, to ensure that developments and land management leave the natural environment in a better state than it was before. It contributes towards nature recovery by helping to deliver habitat creation and enhancements as part of the design of new development.
Measurable BNG provides an opportunity to improve the connectivity of nature on a landscape scale, by promoting more, bigger, better, and joined up habitats. We need BNG because the State of Nature Report (2023) shows that the abundance of 753 terrestrial and freshwater species have declined by approximately 19% in the UK since 1970, and nearly 1 in 6 species (16%) are now threatened with extinction. A collective strategy is therefore necessary to restore and conserve biodiversity.
The information below sets out our response to some common issues and questions about Horsham District Council’s approach to BNG.
What is the minimum level of BNG required?
The law requires that at least 10% biodiversity uplift is delivered in addition to the normal biodiversity mitigation and compensation measures. The Council’s emerging Local Plan has evidence which supports 12% BNG.
How is it measured?
BNG is measured with the support of the statutory biodiversity metric. The metric is a tool to help guide designs and land management decisions that better support biodiversity. The metric subdivides the baseline assessment (determined by UKHab survey and statutory biodiversity metric condition assessments) into three different unit modules based on habitat type. These can be ‘broad’, ‘hedgerow’ or ‘watercourse’ unit modules. Each module is subject to its own 10% net gain in biodiversity, meaning they cannot be interchanged. The catalogued habitats are converted into biodiversity units, which are used as proxy for habitat value, and are calculated using the following information:
Automatically assigned by the metric, ranging from ‘very high’ to ‘low’ based on the national ecological importance of the habitat. Please note that losses of habitat that are assigned as ‘very high’ distinctiveness (for example lowland meadows), will require discussions with Horsham District Council regarding bespoke assessment and compensation.
This is the area of the habitat parcel measured in hectares (or km for linear habitats). This information is inputted by a competent person or ecologist, hereon referred to as the assessor.
A measure of the state of the habitat parcel ranging from ‘poor’ to ‘good’, determined during the UKHab survey by a competent ecologist, in accordance with the statutory biodiversity metric condition assessments, and entered by the assessor into the metric.
Assessors will need to assign strategic significance (the relative importance of the habitat in biodiversity terms, taking account of habitat type and location) for each individual habitat parcel using information published in local plans and strategies. This ensures that habitat creation can be directed to suitable areas, and BNG can contribute to wider nature recovery plans in addition to local objectives.
The assessor will also need to input how much of the various habitats will be retained, enhanced, or lost as a result of the development.
Habitat creation and enhancement plans are entered into the metric on the relevant tabs, and follow the principles of equivalence, i.e., replacing with like-for-like or better habitats.
The metric uses the changes in distinctiveness, extent, condition, and strategic significance to compare the biodiversity value of the proposed post-development habitats with the baseline, to determine if there is a net gain in biodiversity. For more information on how BNG is measured, please visit the User Guide.
How does Horsham District Council consider strategic significance?
Until the West Sussex Local Nature Recovery Strategy (LNRS) is adopted, the following information should be taken into account when assigning strategic significance to habitats.
Habitats considered as having High Strategic Significance are areas depicted within the Council’s Green Infrastructure Strategy and Guide (2024), which includes statutory and non-statutory designated sites, river corridors and features, and the Biodiversity Action Plan (BAP) habitats listed within Sussex Biodiversity Opportunity Areas. Medium Strategic Significance should apply to all priority habitats as well as additional areas (i.e., new sites and buffer sites) mapped within the Wilder Horsham District’s Nature Recovery Network (NRN) report.
From extensive ecological research work, these areas have been identified as having biodiversity value or biodiversity potential, and their ecological functions (will) act as buffer habitats and wildlife corridors across the district. Any other habitats that are deemed ‘ecologically desirable but not in a local strategy’ by a competent ecologist should also be assigned Medium Strategic Significance. All habitats assigned as High or Medium Strategic Significance must be justified as to why they meet this definition within the ‘user comments’ column of the metric. All other habitats that do not fall within the above should be classed as Low Strategic Significance by default.
For more information on how BNG is measured, please visit the statutory biodiversity metric user guide.
What types of development does mandatory BNG apply to?
BNG will become mandatory for all applications submitted on 12th February 2024 for all Town and Country Planning Act (1990) developments, excluding exemptions and small sites.
1) Development impacting habitat of an area below a ‘de minimis’ threshold of 25 square metres, or 5m for linear habitats such as hedgerows and watercourses (excluding priority habitat, listed under Section 41 of the Natural Environment and Rural Communities Act 2006)
2) Householder applications
3) Biodiversity gain sites
- 4) Small scale self-build and custom housebuilding
If a site has a biodiversity unit value of zero, then BNG will not apply. However, developments exempt from mandatory BNG will still need to provide opportunity for biodiversity enhancements in line with local and national policy (Policy 31 of Horsham District Planning Framework 2015 and para 174 of National Planning Policy Framework (NPPF) or any subsequent updates). Applicants should also be mindful of the Council’s emerging Local Plan Policy 17 on Green Infrastructure and Biodiversity.
Small sites are currently expected to deliver mandatory BNG from 2nd April 2024. Small sites are defined by the following:
(i) Residential development: where the number of dwellings to be provided is between one and nine (inclusive), or if this unknown, a site area of less than 0.5 hectares.
(ii) Other development: where the floor space to be created is less than 1,000 square metres or where the total site area is less than one hectare, and is not the winning and working of minerals or the use of land for mineral-working deposits, or waste development.
What biodiversity metric should be used?
For all applications not classed as exempt or small, BNG must be measured using the statutory full biodiversity metric and will need to be completed by a competent ecologist. All sites containing a watercourse (excluding culverts and ditches) will require a River Condition Assessment undertaken by an accredited River MoRPh surveyor.
For small site applications, the statutory small sites metric will need to be completed by a competent person as a minimum requirement (a qualified ecologist is not mandatory, however is advised). In cases where priority habitats, irreplaceable habitats, protected sites, and/or European protected species are present on site, or the habitats on site are not listed within the small site metric, then the full metric must be used. For any off-site interventions as part of small site developments, a full metric will need to be used, and land managers will need to complete the off-site tab.
For more information, please visit the DEFRA guidance on statutory biodiversity metric tools.
Where should BNG be delivered?
It is encouraged that BNG is achieved on-site where possible and ecologically suitable, and this should be a key consideration when designing development proposals. This is in accordance with the biodiversity gain hierarchy, whereby developments need to demonstrate that adverse effects on biodiversity are firstly avoided, then mitigated, and then compensated for on-site, before considering off-site alternatives, which is in keeping with the mitigation hierarchy embedded in the NPPF and set out in BS42020 Biodiversity: Code of Practice for Planning and Development.
For BNG proposed to be delivered off-site, this should be located as close as possible to the development site in order to provide the benefits to local biodiversity and communities. A separate baseline for the off-site area will need to be recorded and entered into the metric. Additionally, a spatial risk multiplier will apply. This means a penalty will be applied to the number of biodiversity units that needs to be delivered, with off-site locations within the Horsham District or the same national character area receiving a lower penalty. Off-site locations outside of these areas will receive a higher penalty, resulting in a higher number of biodiversity units that will need to be offset. It is encouraged that off-site BNG should be directed towards areas considered as High and Medium Strategic Significance, as detailed above.
Please note, where habitat enhancement is proposed on river catchments, the relevant catchment data and river basin management plans should be regarded. Similarly, where habitat enhancements are proposed within protected sites and landscapes, it is advised to consult the appropriate management plans.
Significant on-site and all off-site BNG land will need to be formally registered on the Natural England Biodiversity Gain Site Register. Significant on-site BNG counts as:
*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 biodiversity value of the site before development
*habitat creation or enhancement where distinctiveness is increased relative to the distinctiveness of the habitat before development
*areas of habitat creation or enhancement which are significant in area relative to the size of the development
*enhancements to habitat condition, for example from poor or moderate to good
At present, applicants will need to arrange BNG offsets within their own landholdings or with a third-party, such as landowners and habitat banks. Horsham District Council is unable to provide a list of third-party participants or act as a broker. As a last resort, applicants can purchase credits from the statutory biodiversity credit scheme which go towards habitat creation plans across the UK. However, this will need to be approved by Horsham District Council prior to purchase, and applicants will need to justify how they have rigorously followed the BNG principles and rules.
What information is required to support a planning application?
Upon submission of a planning application, the following information will be required for validation:
*UKHab survey report and GIS mapping, alongside habitat condition assessment sheets (and proven competency of ecologist where appropriate)
*Statutory biodiversity metric in original Microsoft Excel and PDF format
*Habitat Management and Monitoring Plan (HMMP) following CIEEM good practice guidance, where appropriate
The BNG Statement should include:
i)Information about how adverse impacts on biodiversity have been avoided and minimised in accordance with the mitigation hierarchy
ii)Pre-development biodiversity value on-site habitat
iii)Post-development biodiversity value on-site habitat
iv)The proposed approach to enhance biodiversity on-site (including maps)
v)Any off-site BNG plans, including baseline and post-intervention biodiversity values, and maps.
The applicant must make clear, either within the statutory biodiversity metric or BNG Statement, where habitat creations and enhancements are for mitigation or compensation measures up to no net loss, and for BNG. It is advised that two separate metrics be submitted in such cases to demonstrate this.
A draft Biodiversity Gain Plan may be submitted at the validation stage to provide information on how BNG is to be delivered and secured. A finalised Biodiversity Gain Plan, alongside GIS shape files and updated HMMP and biodiversity metric (where appropriate), must be submitted and approved prior to the commencement of the development, as required under the general condition of planning permission (Schedule 7A of the Town and Country Planning Act 1990 and Schedule 14 of the Environment Act 2021). Any off-site land for BNG will need to be registered on the Biodiversity Gain Site Register and allocated to the planning permission before the Biodiversity Gain Plan can be approved.
For phased development, an Overall Biodiversity Gain Plan detailing the baseline and post-development interventions across the whole development must be submitted in as much detail as possible, to give certainty that BNG can be delivered long-term. A Phase Biodiversity Gain Plan for each individual phase detailing the contribution to the overall BNG will also need to be submitted and approved by Horsham District Council before development of that phase can begin.
Using and submitting an Environmental Benefits from Nature Tool is also encouraged to support how the proposed BNG plans will also achieve wider environmental benefits for people and nature.
Please refer to Horsham District Council’s Biodiversity and Green Infrastructure Planning Advise Note for more information.
How is BNG secured?
The monitoring and management of significant on-site and all off-site BNG will need to be legally secured for a minimum of 30 years, although longer agreements may be necessary to ensure more complex habitats reach their target condition. For on-site BNG, it is likely that this will be secured via planning conditions. Other significant on-site and off-site BNG are likely to be secured through S106 agreements and conservation covenants. For more information, please visit the DEFRA guidance on legal agreements to secure BNG.
How is the progress of BNG monitored?
It is the responsibility of the applicant to carry out the monitoring of BNG and to submit reports to Horsham District Council at agreed regular intervals across the stipulated management and monitoring period.
These reports should contain: the BNG targets, an updated UKHab survey and condition assessments; an updated statutory biodiversity metric showing the current biodiversity value of habitats; details of progress towards target conditions and any changes in the habitats since the latest monitoring report; recommendations for changes to the Biodiversity Gain Plan as appropriate, and updated GIS shapefiles where necessary.
The number of monitoring reports will depend on the size, extent, and the type of habitats to be created, and the length of the monitoring period. Typically, reports will be required in years 1, 2, 5, 10, 15, 20, and 30, unless otherwise advised. Horsham District Council will review and verify the reports, and request remedial action be taken where necessary.
As part of the Biodiversity Duty strengthened under the Environment Act 2021, Horsham District Council will use the results and ongoing progress of BNG sites to inform the first full biodiversity report for DEFRA in January 2026. These reports will include a summary of how we have met the BNG obligations, details of BNG resulting (or expected to result) from approved Biodiversity Gain Plans, and how Horsham District Council plans to meet BNG obligations within the next reporting period (5 years).