Habitat baseline / exemptions / statutory metric
How does statutory biodiversity net gain work in Bedfordshire?
BNG compares the biodiversity value of a site before and after development. The statutory biodiversity metric uses the habitats present and their condition, area or length, distinctiveness and other prescribed factors.
First, establish the baseline. Next, assess how the design retains, enhances or creates habitats. The calculation can then show the expected change in biodiversity units and whether a shortfall remains.
A well-prepared assessment should help shape the layout early. For instance, retaining an existing hedgerow can be more realistic than replacing it with new planting and relying on future establishment.
Where the statutory condition applies, the Biodiversity Gain Plan must be approved before development starts. Other supporting information may be required with the planning application itself.
Do all smaller developments need 10% BNG?
No. Statutory exemptions and transitional rules apply.
For qualifying applications made on or after 6 August 2026, developments on a red-line site of 0.2 hectares or less may be exempt if the proposal does not impact on-site priority habitat.
Householder applications have a separate exemption. There are also specific de minimis and temporary-development rules. However, new self-build and custom-build applications no longer have their former general exemption from 6 August 2026.
Use the current national legislation and GOV.UK guidance alongside any separate council biodiversity or ecology requirements.
An exemption from the statutory 10% condition does not remove protected-species duties, local habitat protections or other relevant planning evidence.
Which biodiversity metric should a project use?
Where mandatory BNG applies, the official Statutory Biodiversity Metric or Small Sites Metric, if eligible, provides the required calculation method.
The full Statutory Biodiversity Metric was updated to version 1.1.0 on 3 November 2026. GOV.UK allows qualifying earlier versions of the *statutory* tool, but a pre-statutory Metric 4.0 workbook is not a current statutory calculation.
The correct tool depends on your development and its ecology. In particular, eligibility for the Small Sites Metric is not the same as being exempt from mandatory BNG.
The metric separately assesses area habitats, hedgerows and watercourses. These unit categories cannot simply be added together or used to substitute for one another. Watercourses may also require additional condition assessment and catchment information.
See our Statutory Biodiversity Metric service or Small Sites Metric guidance to understand the appropriate route.