What is biodiversity net gain?
Biodiversity Net Gain (BNG) is a legal requirement for all non-exempt planning applications to demonstrate a 10% net gain for biodiversity.
Introduced as part of the Environment Act 2021, BNG is intended to contribute to tackling the nature crisis currently underway in the UK. As detailed in the State of Nature Report 2023, the UK is now one of the most nature-depleted countries on Earth.
Like the rest of the country, biodiversity in Dorset is in rapid decline. Over 400 land and freshwater species recorded in Dorset in the past are now thought to be extinct. Activities like building, pollution, industrial farming and forestry, and climate change have all contributed to this loss.
Biodiversity Net Gain (BNG) is a key part of the Government's approach to nature recovery. By requiring developments to deliver measurable improvements for biodiversity, BNG creates a legal obligation for habitat creation, enhancement and long-term management. The aim is to deliver more, bigger, better and better-connected habitats, supporting the vision set out in the Making Space for Nature (Lawton Review, 2010) and helping to create a resilient ecological network where wildlife can thrive and recover.
For further information on the current state of biodiversity in the UK, see the State of Nature 2023 report.
This webpage is intended to complement the nationally published guidance on Biodiversity Net Gain and should be read alongside Dorset Council's Validation National and Local List Requirements. It provides additional local guidance to help applicants understand Dorset Council's expectations and the information required to support planning applications affected by BNG.
How is BNG measured?
BNG uses the Statutory Biodiversity Metric Calculation Tool to quantify the value of a site’s habitats using ‘units’ that reflect their relative ecological importance. By comparing the unit values of a site’s existing baseline habitats with its proposed post-development habitats, the net change in value can be calculated. There is a simplified version of the Statutory Biodiversity Metric Calculation Tool, called the Small Sites Metric for small development projects.
For a full outline of the method and the rules which must be complied with for statutory BNG, applicants should refer to the Statutory Biodiversity Metric User Guide on the government website.
Dorset Council requires a minimum 10% net gain consistent with the national statutory minimum.
Pre-application advice
BNG is technical, nuanced, site specific and still quite new. We encourage applicants to engage with the pre-application planning advice service to discuss any BNG queries ahead of making a planning application and avoid delays during the planning process. View the pre-application advice service webpage for more information.
What to submit with a planning application
The Government sets out clear minimum requirements for what information an applicant must provide when submitting a planning application. The minimum requirements are found within the Biodiversity net gain government webpage.
Dorset Council’s local list of validation requirements sets out the information requirements expected to be submitted with each application type. Whilst the statutory minimum requirements for information are limited, the Planning Authority needs to be confident when determining the application that the biodiversity gain condition is capable of being discharged and the biodiversity gains can be delivered.
Additional information may therefore be requested at the planning application stage where there is uncertainty over the capability of the biodiversity gain condition being successfully discharged. The primary reasoning for this could be:
- to have confidence that the Biodiversity Gain Plan will be capable of being successfully discharged post-consent;
- to sufficiently inform any legal agreements or planning obligations that may be required to secure BNG (see on-site significant enhancements below);
- to streamline the discharge of the pre-commencement BNG condition;
Exemptions
Some types of planning application are exempt from BNG, these are outlined in full detail on the Government website for biodiversity net gain and exempt developments.
If applicants wish to claim an exemption, they must submit a supporting justification statement which evidences that their scheme is exempt. Please reference our Local List for further detail.
Significant on-site enhancements
Significant on-site enhancements are defined as ‘areas of habitat enhancement which contribute significantly to the proposed development’s BNG, relative to the biodiversity value before development’. The creation and maintenance of these significant enhancements must be secured with a legal agreement or planning condition for 30 years. The most appropriate mechanism to secure BNG will be agreed during the determination of the planning application.
The Government list of what may count as significant is outlined and listed on the Make on-site biodiversity gains as a developer webpage.
Strategic significance and the Dorset Local Nature Recovery Strategy (LNRS)
Strategic significance is one of the mandatory habitat quality multipliers applied within the statutory biodiversity metric calculation tool. For a full outline of all the multipliers, applicants should refer to the Statutory Biodiversity Metric User Guide on the government website.
The strategic significance multiplier provides a ‘boost’ to the unit value of habitats where they are identified as being locally important for nature conservation. It is divided into three categories: high, medium and low. This multiplier is linked closely with the Local Nature Recovery Strategy (LNRS).
Dorset’s LNRS has been published and is the document that determines the use of the strategic significance multiplier for all applications submitted following its publication in December 2025. In line with Table 7 of the statutory user guide, habitats should be assigned ‘high’ strategic significance if they align with the mapped potential measure in the Local Habitat Map. Any sites located outside of this can only be referenced as ‘low’ strategic significance. (The former ‘medium’ strategic significance category is no longer applicable). For full details and the latest updates applicants should refer to the Dorset's Local Nature Recovery Strategy.
Useful links
Find out more about:
- benefit from our pre-application advice on biodiversity net gain
- government guidance on understanding biodiversity net gain
- a range of biodiversity net gain resources on the Planning Advisory Service website
- what is needed on biodiversity net gain for your planning application in Dorset Council’s validation checklist
- Dorset Council’s work on habitat land banks