Biodiversity Net Gain (BNG) Guidance

Biodiversity Net Gain (BNG) is an approach to development which leaves biodiversity in a better state than before. It encourages development to deliver biodiversity improvements through habitat creation or enhancement and avoiding or mitigating harm. Developers will need to provide an increase in appropriate natural habitat and ecological features over and above that being affected.

In England, biodiversity net gain is becoming mandatory under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021).
Developers must assess the pre and post-development habitat value of their proposals to establish that a minimum 10% gain can be achieved prior to submitting a planning application. The delivery of BNG will be monitored and enforced over a 30 year period.

BNG does not change existing biodiversity protections, statutory obligations, or policy requirements; BNG is in addition to existing wildlife legislation and policy and will be a mandatory requirement to be sequentially introduced as follows:

Major development: 12 February 2024
Small scale development: 2 April 2024
Nationally Significant Infrastructure Projects: November 2025

The Council intends to produce guidance and confirm local policy and validation requirements.

Further information in relation to the requirements can be found through Government Guidance. This is currently being reviewed regularly.

See more information about:

Requirements prior to February 2024
How BNG will apply to existing legislation and policy
How BNG will apply to planning applications
How BNG is measured
Sites cleared prior to the introduction of mandatory BNG
Providing BNG on-site
The off-site BNG market
What BNG information will be required with a planning application
What BNG information will be required prior to commencement
Further information

Requirements prior to February 2024

In the interim period, prior to the mandatory requirements, we will be requesting that all major applications demonstrate that they have sought to deliver no net loss in biodiversity. This can be achieved by use of Natural England’s current Biodiversity Metric. The completed metric should be submitted along with a Biodiversity Statement explaining how no net loss is to be achieved, including pre and post-development habitat plans.

The interim requirement is to accord with sections 174 d) and 179 b) of the NPPF (2023) which refer to the provision of net gains for biodiversity; and Policy GI2 of the City of York emerging new Local Plan, which states that any development should, where appropriate, ‘achieve net gain in biodiversity in accordance with The Environment Act 2021’, as presented in the Main Modifications Schedule (2023).

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How BNG will apply to existing legislation and policy

BNG does not change existing biodiversity protections, statutory obligations, or policy requirements; BNG is in addition to existing wildlife legislation and policy and will be a mandatory requirement for major developments, small sites and nationally significant infrastructure projects.

BNG introduces a quantitative measure to demonstrate a net gain in biodiversity and a framework to secure its implementation. It does not replace the requirement to carry out other assessments of impacts on biodiversity including protected species (for example, bat and great crested newt surveys) or protected habitats (for example, Habitat Regulations Assessments in respect to European Designated Sites). Appropriate licences in respect to derogation of the legal protection given to specific species or sites will still be required where unavoidable impacts are identified.

Compliance with other environmental planning policies will still need to be demonstrated by the developer; these include requirements relating to:

protected or important nature conservation sites
protected or important species
irreplaceable habitats

BNG maintains the mitigation hierarchy with the principles having been built into the technical guidance that accompanies the Metric. In this process adverse impacts on biodiversity should in the first instance be avoided, then minimised or mitigated and, only as a last resort, compensated as follows:

avoidance - actions taken to avoid causing impacts to the environment prior to beginning development (for example, moving the development to a different location, retaining habitats of importance within the design);
minimisation - measures taken to reduce the duration, intensity, extent and/or likelihood of the unavoidable environmental impacts caused by development (for example, adapting the development design to minimise impacts via timing, utilising precautionary working methods);
mitigation/remediation - actions taken to repair environmental degradation or damage following unavoidable impacts caused by development; and
compensation - measures taken to compensate for any adverse environmental impacts caused by development which cannot be avoided, minimised and/or mitigated (e.g. including habitat creation to offset losses).

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How BNG will apply to planning applications

Most planning applications will be required to demonstrate a minimum 10% Biodiversity Net Gain under the Environment Act 2021.
Minor development means:

for residential: where the number of dwellings to be provided is between one and nine inclusive on a site having an area of less than one hectare, OR where the number of dwellings to be provided is not known, on a site area of less than 0.5 hectares.
for non-residential: where the floor space to be created is less than 1,000 m2 OR where the site area is less than one hectare.

Exemptions will be confirmed by secondary legislation, but it is understood that this is likely to include the following:

permitted development
development impacting habitat of an area below a ‘de minimis’ threshold of 25 m2, or 5m for linear habitats such as hedgerows
householder applications
self-build and custom housebuilding, consisting of no more than 9 dwellings, occupying and area less than 0.5 hectares and includes only self-build or custom housebuilding
biodiversity gain sites (where habitats are being enhanced for wildlife)

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How BNG is measured

The Government’s Statutory Biodiversity Metric must be used to measure the biodiversity value pre- and post- development, once BNG becomes mandatory. The Biodiversity Metric is a free biodiversity accounting tool published in Microsoft Excel format, which is used to calculate the change in biodiversity value caused by the change in land use and/or management included within a specific proposal. There are three types of biodiversity units, which are calculated in three separate ‘modules’ of the metric (area units, hedgerow units and watercourse units). A minimum 10% gain must be achieved for each unit type present on site pre-development.

See further information about Statutory Biodiversity Metric tools and guides.

The Biodiversity Metric provides a measure of overall Biodiversity Value based on habitat type, area, distinctiveness, and condition, with an allowance to be made for strategic significance. The metric is a tool that allows the biodiversity value of a site to be measured pre- and post-development. The change in Biodiversity Units indicates either a net loss or net gain in biodiversity. See the definitions of terms that Biodiversity Value is based on:

habitat type: A habitat classification derived from multiple sources, principally the UK Habitat Classification System.
area: The size of the habitat parcel to be retained, enhanced, created, or lost. Size is measured in hectares for area features, or in kilometres for linear features.
distinctiveness*: A value for each habitat type which is pre-set within the metric. It is based on species richness, rarity, the extent to which the habitat is protected by designations and the degree to which a habitat supports species rarely found in other habitats.
condition: Condition is used as a measure of the quality of a habitat, since this can vary between areas of the same habitat type. Condition assessment can be undertaken by a suitably qualified ecologist in accordance with the methodology included within the metric guidance.
strategic significance: Describes the local significance of the habitat based on its location and the habitat type.

The Biodiversity Metric has been designed to follow the mitigation hierarchy and support the retention of valuable habitats. It disincentivises the loss of better-quality habitats by awarding them a higher unit value making them significantly more expensive to provide net gain for, compared to habitats of lower biodiversity value. The replacement of specific habitats of particularly high value, termed ‘irreplaceable’ habitats, is not to be incorporated within the metric and may require that parts of the site are safeguarded from development. More information and a list of ‘irreplaceable’ habitats is awaited from Natural England.

Consequently, it is important to establish the baseline value of a site at as early a stage as possible when considering its development potential, as the loss of higher value habitats or presence of ‘irreplaceable’ habitats may make a scheme unviable.

This work should be undertaken by a suitably qualified Ecologist (relevant institute websites provide directories to identify suitably qualified ecologists including The Chartered Institute of Ecology and Environmental Management and The Institute of Environmental Management and Assessment).

It should be noted that where river units form part of the baseline, river assessments should be carried out by an accredited surveyor. Surveyors will need to have undertaken River Condition Assessment / Modular River Survey (MoRPh) training.

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Sites cleared prior to the introduction of mandatory BNG

Schedule 14 of the Environment Act includes measures that allow the Local Planning Authority to take account of any habitat degradation or destruction undertaken on a site since January 2020. If a site has been cleared or degraded the baseline for the purposes of Biodiversity Net Gain is taken to be that before the clearance or degradation has taken place.

Aerial or other photographs may be used to evidence the habitat types formerly present on site and, in the absence of any other information, the habitat should be allocated a condition score of ‘good’ on a precautionary basis.

This is to deter intentional degradation/destruction prior to planning applications being submitted, by ensuring that there is no advantage to be gained by the deliberate clearance of land to achieve a lower baseline value for BNG with potential penalties where a higher value habitat or condition has to be assumed in the absence of evidence to the contrary.

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Providing BNG on-site

The Environment Act requires proposals to provide a minimum 10% gain compared with the pre-development biodiversity value of the site. Achieving 10% net gain means fully compensating for losses of habitat on a development site, but then going further so that overall, there is a gain in biodiversity value of at least 10% as a result of the development process. The gain can be provided on site, off site or through a combination of the two. As a last resort Statutory Biodiversity Credits, a national credits purchase system will be available for purchase from Natural England. Where Statutory Credits are required, this will need to be agreed with the LPA, prior to approval.

The 10% net gain in biodiversity value should, where possible, be provided on the development site itself. However, where space and circumstances do not allow this, provision of biodiversity gain on land off-site, or a combination of on- and off-site provision, would be considered. Off-site habitat creation can be undertaken on land owned by the developer, or on third party land where the landowner is willing to undertake such work and maintain it for at least 30 years in return for a payment from the developer.

The council will encourage the provision of habitat on-site as a priority with off-site habitat creation/enhancement as a secondary option once appropriate on-site measures have been provided. The Statutory Biodiversity Credit scheme is seen as a last resort option, use of which must be justified by the applicant, and has been priced accordingly to deter use and encourage the development of a local off-site BNG markets.

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The off-site BNG Market

Where developers are unable to provide a 10% Biodiversity Net Gain on-site they can purchase off-site units from third parties either through brokers, habitat bank operators or direct from landowners or land managers.

See more information on from GOV.UK for Information on selling biodiversity units as a landowner or land manager.

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What BNG information will be required with a planning application

The ultimate BNG will be secured by a pre-commencement condition. However, at the point of application, sufficient information will need to be submitted to allow the Authority to be satisfied that an appropriate level of net gain can be provided by the development either utilising on-site land, a combination of on-site and off-site (either developer owned or third party land) or as a last resort, where on-site and off-site provision is unable to provide a 10% net gain, the purchase of Statutory Biodiversity Credits, is being proposed to deliver the outstanding units.

Further guidance from Government and secondary legislation are anticipated shortly to confirm, however, validation requirements are anticipated to be as follows:

the metric calculations (Excel spreadsheet format)
a Biodiversity Net Gain Plan outlining how the development will achieve a minimum 10% net gain, including details of the existing baseline on site habitats, and the anticipated post development habitats retained, created or enhanced to achieve net gain.
GIS mapping demonstrating baseline and post-development habitats
draft monitoring and maintenance plan

We would note that it is accepted that post development habitat plans may be indicative at this stage, particularly with respect to outline applications. However, sufficient detail must be provided to enable the Authority to have confidence that the level of BNG proposed is realistically achievable.

This work should be undertaken by a suitably qualified Ecologist (relevant institute websites provide directories to identify suitably qualified ecologists including The Chartered Institute of Ecology and Environmental Management and The Institute of Environmental Management and Assessment).

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What BNG information will be required prior to commencement

A new statutory pre-commencement planning condition will be used to secure BNG.

The condition will require the submission of a Biodiversity Net Gain Plan, a template for which is due to be published by Natural England. It is anticipated that the plan will be based upon the BNG Statement and Biodiversity Management and Monitoring Plan submitted with the planning application, confirming how the 10% net gain anticipated will be provided, including details of the habitat management to be undertaken to ensure achievement, monitoring and measures to be implemented if the BNG anticipated is not being achieved. Regular monitoring of the habitats will be required, anticipated at years 1, 2 ,3 ,4 ,5, 10, 15, 20, 25 and 30, at which points the developer will be required to submit Monitoring Reports to the LPA which identify whether the intended habitat types and conditions are being achieved and outlining the actions to be undertaken in the next management period in order to rectify any failings. This is to ensure that the Biodiversity Gains proposed with the development are achieved in the long term.

This must then be secured by legal agreement for a minimum period of 30 years. Section 106 agreements are anticipated to be the primary method for securing BNG. However, conservation covenants, a new form of agreement specifically designed for BNG, is being proposed by Natural England between a landowner and a ‘responsible body’ and this may become more widely used as the system develops.

Once the Local Authority has approved the Biodiversity Gain Plan any off-site biodiversity units being used must be registered on a National Register which will be run by Natural England.

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