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Biodiversity Net Gain


Under the Environment Act 2021 and supporting Statutory Instruments Biodiversity Net Gain (BNG) is now mandatory for most development. The legislation requires a minimum 10% gain in biodiversity from applicable development either onsite, offsite or a combination of both.

BNG provided under the mandatory requirements offsite and significant BNG onsite must be secured by a legal agreement for 30 years under an approved Habitat Management and Monitoring Plan (HMMP).

The Council has been applying BNG principles to development since 2019 relying on existing polices and an interim project for offsite net gain provision to require a 10% gain in biodiversity.

The Council’s approach to BNG for all applicable development will now follow the Statutory Instruments and supporting guidance.

This page provides links to the legislation and guidance for developers on BNG as well as providing further guidance relevant to the Borough and the Council’s approach to BNG.

  1. There are strict legal requirements in terms of what an application must contain in relation to BNG before it can be accepted as valid. This is set out in Schedule 7A (Biodiversity Gain in England) of the Town and Country Planning Act 1990 and requires the completed metric calculation tool showing the calculations of the pre-development biodiversity value of the onsite habitat on the date of application and other information.
  2. In addition and in accordance with the PPG Local authority guidance - the Council is setting out what further information it requires in terms of BNG to make an application valid. This will be  set out in the Council’s validation list which is expected to go out for consultation in Spring 2024. In the meantime the relevant extract of the current draft can be found here. The Councils draft validation list requires applicants to submit a Biodiversity Gain Statement.
  3. The Biodiversity Gain Statement, which will include the completed Metric and habitat condition assessment sheets should set out how the development will achieve a minimum 10% gain in Biodiversity through on and/or offsite provision and how such provision will be secured (condition/planning obligation/financially), maintained and monitored for a minimum period of 30 years. A commentary of how the proposals comply with the Biodiversity Gain Hierarchy should also be included. Applicants are advised to use the council’s Biodiversity Gain Statement template.
  4. It will also be helpful to have information about any planning obligation which may need to be entered into connected to the application and the relevant draft heads of term.
  5. Paragraph 13 of Schedule 7A of the Town and Country Planning Act 1990 requires that a Biodiversity Gain Plan (BGP) be submitted and approved to discharge the general biodiversity gain condition prior to the commencement of development. A government template for the Biodiversity Gain Plan can be found here. Applicants may submit a draft of this at application stage instead of the Biodiversity Gain Statement if they wish.
  6. Applicants are generally encouraged to submit as much information on BNG as possible with their application to assist the council with BNG considerations and all material matters that may interact with BNG. Limited information may result in requests for further information and/or delays in determination of an application.
  7. Further information is provided below on particular local matters related to use of the Metric and application of the legislation and guidance. In some cases a lack of information may constitute a reason for refusal.
  1. Certain applications are exempt from the BNG regulations (the Biodiversity Gain Requirements (Exemptions) Regulations 2024) including householder applications and include:
  2. For full details see the Statutory Instrument – the Biodiversity Gain Requirements (Exemptions) Regulations 2024 and PPG – Biodiversity net gain: exempt developments.
  3. The planning application form includes a question on BNG where you are able to state if you think your application is exempt from BNG and provides a drop-down list of reasons for you to select. The Council is likely to require further information to support the exemption reason given especially where it is the de minimis or self-build exemption.
  1. Biodiversity Net Gain (BNG) is an approach to development that leaves biodiversity in a better state than before. Development can produce a biodiversity net gain if it seeks to make its impact on the environment positive, delivering improvements to biodiversity through habitat creation or enhancement after avoiding or mitigating harm.
  2. To arrive at a figure for biodiversity gains and losses that result from development, habitats are converted into measurable units which is done using the Statutory Metric. This uses UKHabs definitions and provides a proxy value for biodiversity that can be measured and monitored and is applicable to all terrestrial and intertidal habitats.
  3. The Statutory Metric has three components which are:
  1. Together these form the statutory element of the metric so that the calculation tool and where required, the condition assessment sheets, must be provided and the guidance followed for the application/metric to be valid.
  2. On smaller sites that are not major the Small Sites Metric (SSM) may be used but there are limitations to what the SSM can cover and so it may not be always be the most suitable choice. Instances where this may be used are set out in the Small Sites Metric (Statutory Biodiversity Metric): User Guide but in summary it can only be used:
  • For residential development where the number of dwellings is between 1 and 9, or if this is unknown, the site area is less than 0.5 hectares
  • For commercial development where floor space created is less than 1,000 square metres or total site area is less than 1 hectare

And the following apply:

  • the habitats on site are available in the SSM
  • There are no priority habitats are present on-site
  • There are no statutory protected sites or habitats present
  • There are no European protected species present
  1. If the Small Sites Metric is used and it subsequently transpires that protected species or priority habitats are likely to be present then the application may be made invalid and the applicant required to submit the main metric before the application can proceed.

Applying Strategic Significance to the Metric

  1. The Statutory Metric User Guide requires that BNG assessors should assign a strategic significance category for each individual habitat parcel (each row of the metric spreadsheet) both at baseline and post-intervention.
  2. The categories are High, Medium and Low which multiply the value of the habitat by 1.15, 1.10 and 1.0 respectively. The values are based on whether the habitat has been identified within a Local Nature Recovery Strategy or in the absence of the LNRS other alternative documents specified by the Local Planning Authority.
  3. In collaboration with all Kent Planning Authorities Kent County Council has published an Interim Strategic Significance Guidance. This must be used to complete the metric and commentary should be provided in the comments column in the metric to explain for each habitat how strategic significance has been applied.

Key Rules and Principles

  1. Information and calculations submitted to comply with BNG requirements will only be accepted where it complies with the rules and principles within the guidance. Key amongst these is the biodiversity gain hierarchy (See PPG Paragraph: 008 Reference ID: 74-008-20240214) which means taking action in the following order of priority:
    • first, in relation to onsite habitats which have a medium, high and very high distinctiveness (a score of four or more according to the statutory biodiversity metric), the avoidance of adverse effects from the development and, if they cannot be avoided, the mitigation of those effects; and
    • then, in relation to all onsite habitats which are adversely affected by the development, the adverse effect should be compensated by prioritising in order, where possible, the enhancement of existing onsite habitats, creation of new onsite habitats, allocation of registered offsite gains and finally the purchase of biodiversity credits.
  2. It is important that developers follow the Biodiversity Gain Hierarchy at every stage including site selection as planning authorities must take into account the Biodiversity Gain Hierarchy when considering whether the biodiversity objective has been met and when determining whether to approve the Biodiversity Gain Plan.
  3. The Biodiversity Metric Rules are set out in table 2 of the User Guide

Table 2 Biodiversity metric rules

Rule Rule detail
Rule 1 The trading rules of this biodiversity metric must be followed.
Rule 2 Biodiversity unit outputs, for each type of unit, must not be summed, traded, or converted between types. The requirement to deliver at least a 10% net gain applies to each type of unit.
Rule 3 To accurately apply the biodiversity metric formula, you must use the statutory biodiversity metric calculation tool or small sites biodiversity metric tool (SSM) for small sites.
The tools remove the need for a user to manually calculate the change in biodiversity value.
The tool will summarise the results of the calculation and inform a user whether the biodiversity net gain objective has been met.
Rule 4 In exceptional ecological circumstances, deviation from this biodiversity metric methodology may be permitted by the relevant planning authority.
  1. As Rule 4 states deviation from the guidance is only applicable in exceptional circumstances which the guidance goes onto explain are exceptional ecological circumstances that must evidenced and agreed with the LPA prior to the submission of the Biodiversity Gain Plan.
  2. The Biodiversity Metric Principles are set out in table 4:

Table 4 Biodiversity metric principles

Principle number Principle detail
Principle 1 The metric assessment should be completed by a competent person.
Principle 2 The use of this biodiversity metric does not override existing
biodiversity protections, statutory obligations, policy requirements, ecological mitigation hierarchy or any other requirements. This includes consenting or licensing processes, for example woodlands.
Principle 3 This biodiversity metric should be used in accordance with established good practice guidance and professional codes.
Principle 4 This biodiversity metric is not a complex or comprehensive ecological model and is not a substitute for expert ecological advice.
Principle 5 Biodiversity units are a proxy for biodiversity and should be treated as relative values.
Principle 6 This biodiversity metric is designed to inform decisions in conjunction with locally relevant evidence, expert input, or guidance.
Principle 7 Habitat interventions need to be realistic and deliverable within a relevant project timeframe.
Principle 8 Created and enhanced habitats should be, where practical and reasonable, local to any impact and deliver strategically important outcomes for nature conservation.
Principle 9

This biodiversity metric does not enforce a minimum habitat size ratio for compensation of losses. Proposals should aim to:

  • maintain habitat extent - supporting more, bigger, better and more joined up ecological networks
  • ensure that proposed or retained habitat parcels are of sufficient size for ecological function
  1. The council would draw applicants attention to principle 1 and the need to use a competent person which would usually be a qualified ecologist with appropriate expertise in the habitats found on site.
  2. Attention is also drawn to Principle 7 that requires that interventions are realistic. The council is for instance unlikely to accept that priority habitats of a high quality can be created and maintained where they are under recreational pressure on a development site, are small in scale or require specialist long term management which is unlikely to be consistently provided.
  3. In addition where native hedgerows and trees are planted in residential gardens these are likely to be treated as part of a vegetated garden area habitats rather than as newly created native hedgerow linear habitats or urban trees.

Habitat Condition Assessments and Plans

  1. The statutory Habitat Condition Assessments are a key part of the metric that needs careful scrutiny. Where applicants consider that a habitat fails to meet certain criteria this may need detailed evidence if it is to be agreed. It is important therefore that original survey data is supplied wherever possible. This is particularly important for semi-improved grasslands where a phase 1 or Preliminary Ecological Appraisal is seldom sufficient to accurately assign a UKHabs grassland type in the metric. For most semi-improved grasslands detailed botanical surveys will be required at an appropriate time of year.
  2. In order for the Council to understand and follow the metric it is important that clear pre and post development plans are provided that have separate ids for each individual habitat area or linear feature that is listed in the metric.
  1. Offsite and significant on site BNG will be secured by legal agreement for a minimum of 30 years managed under an agreed Habitat Management and Monitoring Plan (HMMP) which should ideally follow the Natural England template.
  2. In addition, where long term landscape and biodiversity objectives need to be met by a development, the future management may secured by legal agreement or condition for the lifetime of the development. This may be under a HMMP or a landscape and Ecological Management Plan (LEMP). The LEMP often covers matters beyond what is necessary for a HMMP such as community engagement. One document may cover all that is required but the requirements under BNG for 30 years are likely to be more onerous than the longer-term requirements commonly required under a LEMP and the legal agreement will need to reflect this.
  3. Early discussion on prospective legal agreements is advised to ensure that all matters are correctly dealt with.
  1. Tunbridge Wells Borough Council are working with Kent Nature Partnership and KCC Ecology to continue to develop BNG Policy, practice and guidance.
  2. The council is continuing to develop longer term solutions to off-site BNG that will help strategic BNG objectives.
  3. The council has indicated that it will produce a Biodiversity Net Gain Supplementary Planning Document (SPD) once it has adopted the new Local Plan. The need for a BNG SPD will be kept under review.

For further information please contact:

David Scully
Landscape and Biodiversity Officer

For enquiries about legislation and government guidance on biodiversity, please contact Natural England:

Links to useful government guidance and the statutory metric

Guidance – Information you need for Biodiversity Net Gain (BNG)

Interim Strategic Significance Guidance for Biodiversity Net Gain in Kent

Kent County Council’s Interim Strategic Significance Guidance

Typical LEMP condition for minor development

Prior to first occupation of the dwelling(s) hereby permitted, details of a Landscape and Environmental Management Plan (LEMP) for the site in accordance with BS42020 Biodiversity to include details for the implementation as well as long term management of biodiversity enhancements of the LEMP areas shall be submitted to and approved in writing by the Local Planning Authority. The site shall be maintained in accordance with this plan thereafter for the lifetime of the development.

Typical LEMP Condition for major development

Notwithstanding the submitted details, a Landscape and Ecological Management Plan (LEMP) following the principles set out in British Standard 42020:2013 Biodiversity — Code of Practice for planning and development shall be submitted to, and be approved in writing by, the Local Planning Authority prior to the commencement of above ground construction of the development..

The content of the LEMP shall accordance with council guidance and include the following:

a) Description and evaluation of the landscape and ecological features to be managed and note any features or areas covered by other management agreements or prescriptions e.g. play areas or drainage schemes.

b) Ecological trends and constraints on site and wider environmental issues that might influence management and in particular consider the likely effects of climate change.

c) Landscape and ecological aims and objectives of the management.

d) Appropriate management options for achieving aims and objectives.

e) Prescriptions for management actions for each identified habitat and feature covered.

f) Preparation of a work schedule (including an annual work plan capable of being rolled forward over a five-year period) with recommendations for periodic review.

g) Details of the body or organization responsible for implementation of the plan and the resources both financial and personnel by which the LEMP will be implemented. This shall include details of the legal and funding mechanism(s) by which the long-term implementation of the plan will be secured post development with the management body(ies) responsible for its delivery.

i) Ongoing monitoring and remedial measures including regular review by accredited professionals including setting out (where the results from monitoring show that conservation aims and objectives of the LEMP are not being met) how contingencies and/or remedial action will be identified, agreed and implemented so that the development still delivers the fully functioning landscape and biodiversity objectives of the originally approved scheme.

j) Details of community engagement connected with raising awareness of and/or volunteering for the management of retained and created habitats and features on site for biodiversity..

The approved plan will be implemented in accordance with the approved details.

Reason: To ensure the development delivers ecological net gain in accordance with the requirements of the National Planning Policy Framework, to ensure the development meets the statutory requirement to conserve and enhance the High Weald Area of Outstanding Natural Beauty and to assimilate the development in to the wider landscape.

Typical LEMP requirement in a legal agreement for major development

  1. Landscape and Ecological Management
  2. Prior to Commencement of Development the Landowners covenants that it shall submit to the Borough Council the LEMP and that it shall not first Occupy the Development unless and until the LEMP has been approved by the Borough Council
  3. Content of the LEMP
  4. The LEMP submitted pursuant to this Deed may be varied by a European Protected Species Licence issued by Natural England which must not result in the reduction in the quality or quantity of mitigation /compensation provided.
  5. The LEMP shall include a landscape management strategy which strategy shall as a minimum (and without limitation)

(a) identify describe and evaluate all landscape features of the landscaped areas within the Development 

(b) identify ecological trends and constraints on the landscaped areas within the Development that might influence its management

(c) identify and describe the long term aims and objectives of management and maintenance of the landscaped areas within the Development and how this is to be secured and achieved

(d) where any natural or manmade features are identified in the landscaped areas within the Development including watercourses streams ponds and ditches details to manage and maintain such features shall be provided

(e) prepare and provide a work schedule (including an annual work plan capable of being rolled forward over a 5 year period)

(f) identify the type and source of materials to be used where appropriate (e.g. native species of local provenance)

(g) identify a timetable and the triggers for implementation of the works

AND such other matters as the Borough Council may reasonably require

  1. The LEMP shall also

(a) provide details of the body or organisation responsible for implementation of the LEMP and associated works and include details of the legal and funding mechanism(s) by which the initial aftercare and long-term maintenance of the landscaped areas within the Development shall be secured and delivered by the Landowners

(b) provide for on-going monitoring and remedial measures of the landscaped areas within the Development and on-going species and habitat monitoring which shall include written reports submitted to the council in years 1, 3 and 5 following completion and thereafter at the request of the council.

(c) set out (where the results from monitoring show that conservation aims and objectives of the LEMP are not being met) how contingencies and/or remedial action and measures will be identified agreed and implemented so that the Development still delivers the fully functioning biodiversity objectives of the originally approved scheme

(d) provide for a scheme of community engagement and volunteering in the management of the ecological features of the site organized by a suitable body experienced in such activities consisting of a minimum two events per year.

AND such other matters as the Borough Council may reasonably require