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Biodiversity Net Gain

In line with the Councils declaration of a climate and biodiversity emergency  (Full Council in July 2019 ) the National Planning Policy Framework (NPPF) and Planning Policy in the Submission Local Plan Tunbridge Wells Borough Council are seeking a net gain in biodiversity from all appropriate development. In line with emerging policy and legislation a minimum of a 10% gain in biodiversity is being sought for most developments.

The guidance set out below explains the Councils current position and how it is applying Biodiversity Net Gain (BNG) Policy at the moment. This is interim advice that will be updated to reflect emerging legislation and policy and so should be checked from time to time for updates.

A measurable net gain in biodiversity is required for nearly all development except for householder and advertisements applications, and other minor developments where biodiversity considerations are not appropriate such as some changes of use or minor changes to existing buildings.

The gain in biodiversity shall be demonstrated through the use of the DEFRA biodiversity Metric and submission of a Biodiversity Gain Plan. More details of the DEFRA Metric and how net gain is calculated and further details of what a Biodiversity Gain Plan should include is set out below but here is a check list that may be useful in the preparation of a relevant planning application:

  • Is site survey information on habitats and species accurate and up to date?
  • Does your Plan explain how you have applied the mitigation hierarchy (see figure 1) and any choices made about habitats retained, enhanced or lost?
  • Is there a clear measurable plan of pre and post development habitats with an id reference for each habitat or parcel within a habitat that corresponds with the entry into the metric?
  • Has the metric spread sheet been provided?
  • Is the Plan supported by habitat condition assessment sheets?
  • Is there a proposal for ongoing management and monitoring and how this will be secured?

Mitigation hierarchy

Can significant harm to wildlife species and habitats be avoided?

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Where significant harm cannot be wholly or partially avoided, can it be minimised through mitigation?

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Where, despite mitigation, there would still be significant residual harm, as a last resort, can this be properly compensated for by measures to provide for an equivalent or greater value of biodiversity?

Biodiversity Net Gain

  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.
  1. To arrive at a figure for biodiversity gains and losses that result from development, habitats are converted into measurable units which is done using a Metric. This provides a proxy value for biodiversity that can be measured and monitored and is applicable to all terrestrial and intertidal habitats.
  2. The DEFRA Metric has been developed by Natural England and is cited as the method of calculation in the Environment Act. Guidance on the use of the metric is provided by Natural England (see Biodiversity Metric guidance).
  3. It is acknowledged that there are considerable practical, scientific and philosophical problems with trying to measure biodiversity which is a complex and dynamic system. As such a level of professional judgement is required when assessing the value of BNG units a development may provide and any judgements made in calculating BNG. In addition, other factors such as connectivity, disturbance and protected species are not included within the Metric but need to be taken into account in terms of overall acceptability of a scheme.
  4. This guidance sets out the Councils approach to both use of the metric and its approach to these other factors.  It is intended to assist applicants as an interim measure whilst we await the publication of Secondary Legislation for the Environment Act and as a precursor to specific Supplementary Planning Guidance for BNG.
  5. It is important to note that achieving gains in biodiversity from the calculation does not necessarily mean a development meets any wider requirements of planning policy or law relating to nature conservation or biodiversity.
  1. The Council’s current adopted policy for Biodiversity (CP4) is “no net loss” but the more recent National Planning Policy Framework (NPPF) paragraphs 174(d) and 179(b) require development to provide measurable net gains for biodiversity which is supported by the Government’s 25-year Environment Strategy.
  2. The Environment Bill which received Royal Assent on 9 November 2021 and the Councils emerging policy (Policy EN9: Biodiversity Net Gain) on BNG require a minimum 10% gain in biodiversity in both area and linear units as measured using the DEFRA Metric.
  3. The Council’s current position is that it will seek BNG in general conformity with the emerging policy in the Submission Local Plan (Policy EN9: Biodiversity Net Gain):
  4. Policy EN 9: Biodiversity Net Gain

    Development will only be permitted where it meets all of the following criteria:

    1. It can be demonstrated through the application of the Defra Biodiversity Metric (and any subsequent replacements), as part of a Biodiversity Gain Plan, that completion of the development will result in a long-term net gain for biodiversity in both area and linear habitats, as follows:
      1. net gain shall be provided on, or adjacent to, the site wherever possible and where provided off-site shall, in terms of location and type, be in accordance with the supporting text or as otherwise required by supplementary planning guidance;
      2. the percentage of net gain shall be a minimum of 10% as required by legislation or greater where required by supplementary planning guidance;
      3. the Biodiversity Gain Plan will include, as a minimum, the information set out in the supporting text or as otherwise required by supplementary planning guidance;
    2. It can be demonstrated that the proposals have adopted a strict approach to the
      1. mitigation hierarchy (i.e. avoid, mitigate, compensate) and are able to justify all
      2. unavoidable impacts on biodiversity;
    3. The proposed mitigation, compensation, and/or enhancement measures required to secure net gain for biodiversity are acceptable to the Council in terms of design and location, and are secured, on-site, for the lifetime of the development, or off-site for a minimum of 30 years, with appropriate funding mechanisms that are capable of
      1. being secured by condition and/or legal agreement. Funding for both on-site and
      2. off-site measures shall include a payment to the Council to cover the costs of
      3. independent review of Biodiversity Gain Plans and long-term monitoring.
  5. The Council is committed to producing a Supplementary Planning Document (SPD) on BNG and is working with key stakeholders to develop the SPD. This advice note sets out how BNG matters will be dealt with in the interim and covers:
    • When BNG is required
    • What an application should include for BNG
    • How the Council will review submitted BNG reports and completed metrics
    • How BNG will be secured within a Planning application
    • TWBC’s interim Strategy and next steps.
  1. Biodiversity Net Gain will apply to all applications, except for householder and advertisements applications, and other minor developments where biodiversity considerations are not appropriate, e.g. a change of use from Class E (retail) to Sui generes takeaway and those submitted as prior notifications pursuant to the General Permitted Development Order.  Those developments not covered by Policy EN 9: Biodiversity Net Gain may still contribute to net gain through, where appropriate, through the attachment of a planning condition to any consent requiring a scheme of ecological enhancements.
  2. Where a site has very little or nil biodiversity value such as a highly urbanised site/building proposed for redevelopment applicants should still explore ways of improving biodiversity through green roofs and walls or trees and shrubs in paved areas/containers.
  3. The Council will expect developers to provide mitigation, compensation, and enhancement measures for biodiversity on, or immediately adjacent to, a site for all major development proposals (10 dwellings plus, 1,000sqm plus of floorspace, new build, or conversion or outline proposals capable of accommodating either.) Only in exceptional circumstances and in the interests of biodiversity will ‘off-site’ proposals be considered acceptable. For non-major development on-site, mitigation, compensation, and enhancement measures will be the preferred option, but off-site or offsetting will be considered where it offers the best outcome for biodiversity, is in reasonably close proximity to the application site and follows the mitigation hierarchy.
  4. Only that which cannot be mitigated or compensated for on-site will be permitted off-site, so even where off-site is agreed, on-site measures will still be required.
  5. Biodiversity will be calculated using the Defra Metric 3.1 or for small sites the Defra Small Sites Metric or any subsequent versions. Small sites are defined as:
    • For residential development 9 dwellings or less on a site having an area of less than one hectare or where the number of dwellings to be provided is not known the site area is less than 0.5 hectares
    • For all other development types where the site area is less than 0.5hectares or less than 5,000sqm
  6. Please notes that the Small Sites Metric cannot be used where priority habitats are present within the development area (excluding hedgerows and arable margins).
  7. BNG shall be calculated for both Outline and Full applications. BNG calculations shall also be resubmitted for any reserved matters application or material amendment that is likely to affect BNG.
  1. The results of the calculations using the Defra Metric should be set out in Biodiversity Gain Plan in accordance with the prevailing Natural England guidance and should include:
    • Survey Information
    • Baseline Habitat Plans
    • Post Development Habitats Plans
    • Findings and Calculations
    • Matters outside the metric
    • Implementation
    • Management

  2. Survey Information: The surveys should accord with current best practice and be conducted by a suitable professional using the UK habitats methodology to level 4 or, where appropriate, level 5. As this is a habitat-based system surveys should be carried out by professionals that have the appropriate experience and expertise for the habitats found on a particular site. Where Phase 1 or other survey data is used there should be a clear explanation of how its has been translated into UK Habitats data.
  3. Condition assessment sheets for each habitat listed in the Metric should be provided. Where there is any uncertainty or variability across a habitat that makes habitat classification or condition assessment difficult the metric shall be run using a range of possible inputs and the results recorded as a range of possible outputs or the habitat should be subdivided according to the variation in condition. Particular attention will be given to grassland surveys in terms of timing and condition to ensure that the classification and condition score properly reflect the habitat present.
  4. Where there are limitations to surveys including when they are at a sub-optimal time of year a precautionary approach should be taken to condition scoring.
  5. Baseline Habitat Plans: A accurate, measurable baseline habitat plan(s) is required for all existing habitats.  Each habitat or habitat parcel should have a unique id shown on the plan as input and referenced in the metric spread sheet.  For each area identified in the metric there should be a completed corresponding habitat condition assessment sheet with clear reasoning for any fails in the assessment criteria.
  6. Post Development Habitat Plans: an accurate, measurable plan of proposed habitats as referenced in the metric. Each habitat or habitat parcel should have a unique id shown on the plan as input and referenced in the metric spread sheet.   For retained habitats to be enhanced or converted to other habitats then further information may be needed to support the proposal to ensure that it is deliverable.  This may include soil and hydrological surveys and/or detailed methods of cultivation.
  7. Findings and Calculations: The Biodiversity Net Gain Plan should include a summary of the findings of the Metric and be supported by the actual metric spread sheet. The Plan should explain why particular habitats have been chosen and any deviation from published guidance and any uncertainties with the results.
  8. Matters outside the metric: The Biodiversity Gain Plan should also set out those biodiversity matters both negative and positive that are outside the scope of the metric including wider ecological enhancements and or species mitigation measures such as, bird boxes, bat boxes, gaps in close board fences for hedgehogs, bee bricks, and deadwood features. It should also include consideration of likely indirect effects such as disturbance and any risks associated with the proposals.
  9. Implementation: Details should be provided of how the development will be implemented with regards biodiversity including setting out how existing habitats will be protected, how development will be controlled, and how the measures will be secured to the development. This is likely to include detailed drawings, detailed landscape planting schedules, management proposals and/or a construction handover checklist and the timetable for implementation.
  10. Management: Details of how retained, enhanced and created habitats will be monitored and maintained, and by whom and how the work will be funded and who will ultimately be responsible.  The Council will in most circumstances require a Landscape and Ecological Management Plan (LEMP) secured by condition and/or legal agreement.
  1. The Council will review all survey data, and the Biodiversity Gain Plan and do checks on the Metric and where necessary undertake further detailed analysis. Any concerns or noted discrepancies will be discussed with the applicant and the Council will seek to agree the most likely figure or range of figures for net gain.
  2. In the event of any agreed shortfall in net gain below 10% the Council will review the justification for this and seek to agree how any shortfall is made up from an off-site provision.  At the present time, the Council is able to offer an interim proposal for off-site provision and details of this scheme are provided below. Other proposals for off-site provision will be considered but will need to be suitably evidenced and secured to the planning consent.
  3. In its considerations of a Biodiversity Gain Plan the Council will use its professional judgement to come to a view on:
    • The confidence in the predicted type and condition of post development habitats
    • The identification of and the mitigation for any other effects on species or habitats not covered by the metric such as disturbance or pollution.
    • Whether the application includes other benefits to biodiversity not included within the metric that may be taken into account as part of an overall planning judgement such as longer-term security for offsite habitats or additional measures that improve outcomes for biodiversity on or adjacent to the development e.g., education or volunteer programmes.
  1. For major developments BNG will be secured by legal agreement and condition. Land on or adjacent to a development that provides for landscape and ecological benefits including BNG will be covered by a Landscape and Ecological Management Plan (LEMP) defined within a condition or legal agreement with the area to which the LEMP applies covered by an agreed plan. Smaller schemes may be covered by condition only.  For examples of conditions please see Appendix A.
  2. For non-major development, such matters will be covered by condition.
  3. Where an off-site provision for BNG is required this will be covered by a legal agreement.  Where this involves a contribution to the Council’s Interim Strategy for BNG the Contribution in the legal agreement will be referred to as the Biodiversity Net Gain Off Set Project and will be defined as:

    “the Borough Council endorsed interim strategy for biodiversity net gain “Net gain for Biodiversity in the Borough 2019” which includes developing a local scheme of biodiversity offsetting and specifically improvements to biodiversity on land owned by the Borough Council at Marshley Harbour Snipe and Bassetts Woods located in Pembury and High Woods located in Hawkenbury and which shall be funded through financial contributions made by developers and landowners who are unable to provide on-site measures to increase biodiversity and which shall include measures including but not limited to the implementation of biodiversity focused management of the woodland, improved provision for access to local people and timber management”

  1. In order to ensure that development is not held up where an off-site provision of biodiversity is necessary and appropriate the Council has developed an interim strategy for providing BNG (Cabinet 12 September 2019 ) allowing developers to pay into a scheme that will provide BNG and contribute towards developing a longer term strategy. The scheme is voluntary but where an applicant wishes to propose an alternative off-site provision this will need to be assessed and approved by the Council to ensure it complies with the core principles of BNG and the emerging legislation and policy.
  1. TWBC are working with Kent Nature Partnership to develop BNG Policy and guidance and to develop longer term solutions to off-site BNG that will help strategic BNG objectives.
  2. The government is producing secondary legislation to support the Environment Act and there are likely to be further updates and guidance for the DEFRA Metric which the Council will need to take into account.
  3. A Biodiversity Net Gain Supplementary Planning Document will be drafted to reflect this work and the outcome of work on a longer-term strategy for off-site BNG.

For further information please contact:

David Scully
Landscape and Biodiversity Officer

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:

  1. 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.
  2. Ecological trends and constraints on site and wider environmental issues that might influence management and in particular consider the likely effects of climate change.
  3. Landscape and ecological aims and objectives of the management.
  4. Appropriate management options for achieving aims and objectives.
  5. Prescriptions for management actions for each identified habitat and feature covered.
  6. 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.
  7. 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.
  8. 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.
  9. 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
    1. 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
  2. Content of the LEMP
  3. 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.
    1. The LEMP shall include a landscape management strategy which strategy shall as a minimum (and without limitation)
    2. identify describe and evaluate all landscape features of the landscaped areas within the Development
    3. identify ecological trends and constraints on the landscaped areas within the Development that might influence its management
    4. 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
    5. 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
    6. prepare and provide a work schedule (including an annual work plan capable of being rolled forward over a 5-year period)
    7. identify the type and source of materials to be used where appropriate (e.g. native species of local provenance)
    8. identify a timetable and the triggers for implementation of the works

      AND such other matters as the Borough Council may reasonably require
    9. The LEMP shall also
      1. 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
      2. 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.
      3. 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
      4. 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