Biodiversity Net Gain

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Biodiversity Net Gain

Biodiversity net gain (BNG) is now mandatory for all Town and Country Planning Act development bar exempt development types.

Under the Environment Act 2021, all planning permissions granted in England (with a few exemptions) will have to deliver at least 10% biodiversity net gain. 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 habitat of at least 10% as a result of the development process. The Government is introducing this requirement to help meet its aspiration to leave the environment in a better state than it found it, and to help meet targets for nature recovery required under the Environment Act.

The biodiversity net gain approach embeds a fundamental principle for the spatial hierarchy of habitat delivery, where there is a preference for onsite or local enhancements. Where a development cannot achieve BNG either wholly or partly onsite, then the developer can secure the unit shortfall by securing a bespoke site for net gain, or from appropriate sites on the local net gain habitat market from other landowners. If a shortfall in units required to achieve BNG remains, having explored the onsite and local offsite options, a developer can purchase statutory biodiversity credits from government as a last resort. When offsetting offsite is it the applicant’s responsibility to find suitable sites.

In relation to BNG, the Environment Act states that habitats should be secured for a minimum of 30 years: ‘habitat enhancement… will… be maintained for at least 30 years after the development is completed’.

Exempt Development Types

The general biodiversity gain condition does not apply to the following types of development:

  • Householder development as defined within article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015.
  • Development granted planning permission by a development order under section 59 This includes permitted development rights.
  • Development subject to the de minimis exemption - development that does not impact a priority habitat and impacts less than 25 square metres (e.g. 5m by 5m) of habitat, or 5 metres of linear habitats such as hedgerows.
  • Self-build and custom build development - development which: consists of no more than 9 dwellings, and is carried out on a site which has an area no larger than 0.5 hectares, and consists exclusively of dwellings which are self-build or custom housebuilding as defined in section 1(A1) of the Self-build and Custom Housebuilding Act 2015.
  • Urgent Crown development granted under s293A TCPA 1990.
  • Development of a biodiversity gain site - development which is undertaken solely or mainly for the purpose of fulfilling, in whole or in part, the biodiversity gain planning condition which applies in relation to another development.
  • Development related to the high speed railway transport network - development forming part of, or ancillary to, the high speed railway transport network comprising connections between all or any of the places or parts of the transport network specified in section 1(2) of the High Speed Rail (Preparation) Act 2013

Delivering net gain is independent of any wider requirements of planning policy or the need to comply with legislation relating to nature conservation or biodiversity.

Exempt development outside the scope of mandatory net gain still provides opportunity for biodiversity enhancements that could be secured through planning policy.  The Ipswich Wildlife Audit provides information and a description of the wildlife interest for each survey site and recommendations for biodiversity enhancements.

Submitting a Planning Application

Where development would be subject to the general biodiversity gain condition, the application must be accompanied by minimum information set out in Article 7 of The Town and Country Planning (Development Management Procedure) (England) Order 2015:

  • a statement as to whether the applicant believes that planning permission, if granted, would be subject to the biodiversity gain condition;
  • the pre-development biodiversity value of the onsite habitat on the date of application (or an earlier date) including the completed metric calculation tool used showing the calculations, the publication date and version of the biodiversity metric used to calculate that value;
  • where the applicant wishes to use an earlier date, the proposed earlier date and the reasons for proposing that date;
  • a statement confirming whether the biodiversity value of the onsite habitat is lower on the date of application (or an earlier date) because of the carrying on of activities (‘degradation’) in which case the value is to be taken as immediately before the carrying on of the activities, and if degradation has taken place supporting evidence of this;
  • a description of any irreplaceable habitat (as set out in column 1 of the Schedule to the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations [2024]) on the land to which the application relates, that exists on the date of application, (or an earlier date); and
  • a plan, drawn to an identified scale which must show the direction of North, showing onsite habitat existing on the date of application (or and earlier date), including any irreplaceable habitat.

If this information has not been provided, the local planning authority must refuse to validate the application. Within the planning application form applicants will be asked to confirm whether this information accompanies the application. Where these details have been provided elsewhere in accompanying documents, applicants are encouraged to refer to these rather than duplicate this information within the application form.

In addition to these minimum information requirements, further information may need to be provided in order to assist the consideration of biodiversity net gain as part of the planning application, in particular where there are particular considerations around significant onsite biodiversity enhancements or use of offsite biodiversity gains.

Sites with a Baseline Value of Zero

If a site has a baseline biodiversity unit value of zero, then it would be exempt from mandatory BNG, but planning policy requirements for net gain would still apply.

It should not be assumed that just because a site is small/in an urban setting/been previously developed it has no baseline value. The baseline value reflects the ecological value of the pre-development site, not its size.

Competent Person

The metric calculations and associated reporting as well as the development of habitat creation to achieve net gain will need to be undertaken by a 'competent person'. A competent person is defined as: being able to confidently identify the positive and negative indicator species for the range of habitats likely to occur in a given geographic location at the time of year the survey is undertaken. This definition comes from the Planning Advisory Service (PAS). For a full metric application, the competent person should be an ecologist.

Watercourse habitat types (excluding culverts and ditches) use different condition assessment methodologies. To undertake a river condition assessment the competent person must be trained and accredited to conduct a river condition assessment. 


The 10% BNG set out in legislation is mandatory and therefore there is no scope for LPAs to allow a reduction on viability grounds.

The Biodiversity Metric has been designed to disincentivise the loss of high-quality habitats to development, by making them significantly more expensive to provide net gain for compared to lower value habitats.

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 may make a scheme unviable or may require that parts of the site are safeguarded from development to enable an economically viable scheme to be developed.

Deliberate Degradation of Habitat

The Environment Act includes provisions in Schedule 14 that allow the Local Planning Authority to consider any degradation or destruction of habitats on a site since January 2020 when determining biodiversity net gain. This provision is intended to prevent any advantage gained through land clearance to achieve a lower baseline value for biodiversity net gain.

In cases where habitats on a site have been destroyed or degraded prior to a survey and submission of a planning application, the earlier state of the habitat will be considered the baseline for the biodiversity metric.

Relevant Biodiversity Net Gain Regulations

More Information