Biodiversity Net Gain Update for Agents and Developers

The introduction of mandatory biodiversity net gain (BNG) marks a significant change in the way in which ecological matters are addressed through the planning process, and its introduction will present significant challenges A range of guidance concerning biodiversity net gain has been provided by Government; it is not the intention of this guidance to replicate or replace that. It is simply to highlight some key issues and set out some local issues such as local information requirements for planning submissions.

Our understanding of how BNG will work in practice is still evolving as various matters are clarified by government and case law. Accordingly, this guidance is likely to be updated quite frequently and so it is important to look at our pages to ensure that you are referring to the current version. We have tried to keep our guidance consistent with Northumberland County Council’s guidance to ensure consistency across the whole county.

Commencement dates

BNG becomes mandatory for applications for major development submitted on or after 12 February 2024 and for applications for minor development submitted on or after 2 April 2024. Minor development is defined as residential sites of no more than 9 dwellings or sites of less than 0.5ha where number of dwellings is unknown; and non-residential schemes where the floorspace is less than 1000 m2 or the site is less than 1ha in size. The majority of applications received by the National Park Authority would fall as minor development.


The following types of development are exempt from the BNG requirement:

  • Householder development.
  • Permitted development.
  • Development subject to the de minimis exemption. Defined as development that does not impact a priority habitat and impacts less than 25m2 of habitat, or 5m of linear habitats such as hedgerows.
  • Self-build and custom build development. Development which:
  • Development of a biodiversity net gain site, where that requires planning permission.

Variations and reserved matters are exempt if the original or outline application was submitted prior to the relevant commencement date above.

The GOV.UK website shows the full list of exemptions.

One of the Parks haymeadow habitats

The BNG process

The Town and Country Planning Act has been amended to make every grant of planning permission deemed to have been granted subject to the following planning condition:

The development may not be begun unless:

  1. a biodiversity gain plan has been submitted to the planning authority; and
  2. the planning authority has approved the plan.

The purpose of the condition is to secure the biodiversity objective, which is that the biodiversity value attributable to the development exceeds the pre-development biodiversity value of the onsite habitat by at least 10%. This can be achieved through habitat creation or enhancement onsite; the provision or purchase of biodiversity units from a habitat bank; or in a last resort through the purchase of statutory credits; or a mixture of these.

However, although final information may only be required through the discharge of a pre-commencement condition, BNG is a material consideration when determining applications. The LPA needs to understand how the BNG requirement is to be met prior to determining the application, so that necessary planning conditions can be imposed and/or S.106 Agreements signed. This is made clear in paragraphs 015 of the Planning Practice Guidance for Net Gain . Accordingly, extensive information is still required at the application stage, as set out below.

National validation requirements

The following national validation requirements have been imposed:

  • A statement as to whether the applicant believes the development is subject to the biodiversity gain condition (on application form).
  • A biodiversity metric showing the pre-development biodiversity value of the onsite habitat on the date of application.
  • A statement confirming whether the biodiversity value of the onsite habitat is lower on the date of application because of the carrying out of activities (‘degradation’).
  • A description of any irreplaceable habitat.

A plan showing onsite habitat existing on the date of application.

If this information has not been provided, the local planning authority must refuse to validate the application.

Bellcrag flow peat bog
Bellcrag flow, a mire or blanket bog in Wark Forest, Northumberland National Park, England. OS grid reference NY 777 726

Local information requirements

A Biodiversity Net Gain Strategy will be required, setting out how 10% BNG will be achieved. This must include a completed draft metric for the proposed scheme, and information addressing the following points:

  • How the mitigation hierarchy has been followed.
  • How the Metric Principles and Good Practice Principles are being adhered to.
  • How the BNG hierarchy has been followed if you have any habitats of medium distinctiveness or higher on site.
  • Whether proposals for onsite habitat creation or enhancement are appropriate, taking account of other requirements for greenspace within a development.
  • How any need for offsite units will be met.
  • Whether you have an excess of onsite biodiversity units that you intend to use for other developments or sell to the market.

This must be prepared by a professional ecologist with suitable qualifications and experience and be in accordance with the British Standard BS8683 ‘Process for designing and implementing biodiversity net gain – specification’.

These requirements will be added to NNPA’s Local Validation List at the next review. Until then they are advisory; however, without this information the Authority may be unable to determine the application other than by refusing it on the grounds of insufficient information.

The decision notice

Because the general biodiversity gain condition has a separate statutory basis to other planning conditions and is deemed to apply to all planning permissions other than specifically exempted ones, LPAs have been instructed not to include it in the list of conditions imposed in the decision notice. Instead, the decision notice will include information about BNG, for which DLUHC will provide model paragraphs.

Discharging the BNG condition

Development cannot be commenced until the mandatory BNG planning condition has been discharged. To discharge the condition, the following information must be submitted:

  • A completed biodiversity metric.
  • A Biodiversity Gain Plan setting out how the biodiversity gain objective of at least a 10% gain will be met for the development.
  • For habitat being created on the development site, a Habitat Management and Monitoring Plan setting out how the habitat will be managed for at least 30 years, and how this will be monitored.
  • Pre-development and post-development plans showing the location of on-site habitat.
  • If the developer is purchasing units from a Habitat Bank – the reference number from the Biodiversity Net Gain Register.
  • If the developer is purchasing statutory credits – proof that they need them and proof of purchase.

The following templates have been created by Natural England. These must be used unless otherwise agreed with the LPA.

Biodiversity gain plan template

Habitat management and monitoring plan template

Multistage development

The Biodiversity Gain (Town and Country Planning) (Modifications and Amendments) (England) Regulations 2024 modify the general biodiversity condition for planning permissions which are phased development. Instead of the standard approach for the Biodiversity Gain Plan:

  • an Overall Biodiversity Gain Plan must be submitted to and approved by the planning authority before any development can be begun.
  • a Phase Biodiversity Gain Plan for each phase must be submitted to and approved by the planning authority before the development of that phase can be begun.

In recognition that phased development can often be implemented over a long period of time, the purpose of the Overall Biodiversity Gain Plan is to set a clear upfront framework for how the biodiversity gain objective of at least a 10% gain is expected to be met across the entire development. Each Phase Biodiversity Gain Plan will subsequently set out a phase’s contribution to biodiversity net gain and track progress towards the overall biodiversity gain objective for the development once clear proposals for each phase have been developed.

It is envisaged that, for an outline planning permission for phased development, the Phase Biodiversity Gain Plan would be prepared alongside the application for reserve matter approvals for a phase. Further details can be found in the Planning Practice Guidance for Biodiversity Net Gain.

Submitting the BNG Metric as part of your planning application

Submitting the BNG Metric as part of your planning application and discharge of conditions application

Please note that Section 9 of the Metric User Guide states that the metric should be submitted as a macro disabled Excel file. This is because the Planning Portal cannot handle macro-enabled files.

A view of Shillmoor Farm, Green Side and Pass Peth
Shillmoor Farm, Green Side and Pass Peth, Northumberland National Park, England

Important issues when planning how to meet your BNG requirements

Good ecological outcomes and the mitigation hierarchy

While the introduction of a metric that generates numerical values to quantify losses and gains of habitats is one of the most striking aspects of Biodiversity Net Gain, the metric is only a tool to help to estimate the value of what is being proposed. The purpose of Biodiversity Net Gain is to require development to have a positive impact on biodiversity overall through the creation and enhancement of habitats, and so at every stage of the process it is essential that ecological principles are being followed and the process is being considered in terms of how to achieve best outcomes for nature rather than just best numbers in the metric.

Importantly, the mitigation hierarchy set out in paragraph 186a of the NPPF remains paramount – harmful impacts must first be avoided. Where they are unavoidable, they must be adequately mitigated, with compensation being a last resort. Enhancement should then be secured over and above that. Accordingly, the net gain process can be seen to apply right at the end of that process – to the compensatory and enhancement stages. It does not remove the need to avoid impacts as the first priority.

To help ensure that good ecological outcomes are secured through the Biodiversity Net Gain process. A series of nine metric principles are set out in section 3 of the Metric User Guide. In addition to the four metric rules that must in all circumstances all be adhered to. The principles exist to ensure that expert ecological advice and established ecological principles are always used throughout the BNG process. CIEEM, IEMA and CIRIA have produced a guide called Biodiversity Net Gain: Good Practice Principles for Development. It provides extensive advice to ensure that best ecological outcomes can be secured through the BNG process.

The use of the biodiversity metric does not override existing biodiversity protections, statutory obligations, policy requirements, ecological mitigation hierarchy or any other requirements.

Interim arrangements for the strategic significance section of the metric until the North of Tyne Local Nature Recovery Strategy is published

Strategic significance relates to the spatial location of a habitat parcel and it operates at a landscape scale.  All habitat parcels (both baseline and post-intervention) must be assigned a strategic significance score; it should be considered separately for each individual habitat parcel in the metric and not on a site-wide basis. Habitat not specified in some form of strategy, map or plan for that area should not be considered strategically significant.

The options for scoring each habitat parcel are:

High strategic significance – Formally identified in local strategy, plan or policy (this decision must be justified in the ‘Assessor comments’ section of the metric calculation tool). Until the LNRS is available, the following sources of evidence can be used to identify sites of high strategic significance:

On the Baseline Tab

  • Land adjacent to Habitats of Principal Importance.
  • Land adjacent to designated sites (SSSIs, Local Wildlife Sites, Local Nature Reserves.
  • Land partly or wholly within the Southeast Northumberland Wildlife Network.

On the Habitat Enhancement and Habitat Creation Tabs

  • Land adjacent to Habitats of Principal Importance on which it is proposed to create habitats of types compatible with the adjacent HPI.
  • Land adjacent to designated sites (SSSI, Local Wildlife Site, Local Nature Reserve) where the habitats proposed to be created are compatible with the interest features of the designated site. Similarly land within Local Wildlife Sites where proposed enhancement will improve the condition of the LWS.
  • Proposals that support the Southeast Northumberland Wildlife Network by creating or enhancing habitat within or immediately adjacent to this.

HPI can be found on the DEFRA Magic mapping website. Go to Habitats and Species / Habitats / Other / Priority Habitats Inventory.

Boundaries of SSSIs, Local Wildlife Sites, Local Nature Reserves and the Southeast Northumberland Wildlife Network can be found under Local Plan Policy ENV 2 on the Northumberland Development Plan Policies Map.

Medium strategic significance – location ecologically desirable but not identified in a local strategy, plan or policy.

Professional judgement is applied, and the location is deemed ecologically desirable for a particular habitat type, whether recorded in the site baseline, being created or enhanced. The decision should be justified, and evidence provided in the ‘Assessor comments’ section of the metric calculation tool.

Low strategic significance – all other sites.

Provision of BNG on the development site

In principle, the development site itself is the preferred location for the created or enhanced habitats that will satisfy the BNG requirement, so that there isn’t a spatial separation between where habitats are being lost and where they are being established, and to ensure that local communities benefit from a nature-rich environment. However, there are significant issues to be considered when determining whether this is realistic, especially on large residential sites. Inevitably open space is going to be used by local residents for a range of uses such as informal play and exercise, including dog-walking. This imposes some extra considerations on top of the normal considerations such as soil nutrient status in determining what habitats could realistically be sustained and managed, and what condition could realistically be achieved for those habitats.


Once they have been created, the habitats will need to be managed for a 30-year period, during which a monitoring process will be used to determine if the required gains are being achieved and to identify remedial measures if not, and so it is in everyone’s interests to ensure that BNG proposals are realistic and achievable.

Meeting the BNG requirement through the purchase of biodiversity

A number of landowners in Northumberland County are establishing Habitat Banks – areas of land where they will create or enhance habitat in order to be able to sell biodiversity units to developers.

In order to do this, they will need to conclude legal agreements with the Authority where they are based and then register the sites with Natural England. If the sites are within the National Park, the Authority will maintain a list of registered sites so that it is straightforward for developers to find local providers. There will also be a list for sites within Northumberland County Council area.

Meeting the BNG requirement on other land owned by the developer

If a developer intends to satisfy their BNG requirements on land that they own outside of the red-line boundary of their development site, they will need to sign a S.106 Agreement with NCC and then register the offsite area with Natural England, following the same process as for Habitat Banks.

Contact details

To discuss specific BNG relating to a site within the National Park Authority, we would recommend engaging with our pre-application service, details of which can be found here: