The Department for Environment, Food and Rural Affairs (DEFRA) introduced biodiversity net gain (BNG) as a way of ensuring that developers are environmentally minded when undertaking projects.
The idea was to create a clear framework to ensure that new major infrastructure developments left biodiversity in a measurably better state than before the development took place, in alignment with the legally binding Environment Act 2021 targets for biodiversity.
This has had significant, but unforeseen consequences for SMEs in the development sector. The government has recognised this issue and on 28 May, DEFRA published a consultation on the implementation of biodiversity net gain for minor, medium and brownfield development. This consultation closes on 24 July 2025.
What are the key proposals of the consultation?
Exemptions
The consultation proposes making targeted revisions to the existing exemptions, introducing a full exemption for all minor developments or introducing additional exemptions for developments with conservation aims, temporary permissions or minimal land use change. Minor developments are defined as sites under ten dwellings or less than 0.5 hectare if no number is known.
Replace the self-build exemption
The consultation proposes to replace the self-build exemption with one for a single dwelling on small sites (those less than 0.1 hectares) as well as options for a higher de minimis threshold from 25m² to 250m² so that more minor development would be exempt in practice.
Simplify requirements
The consultation also aims to simplify BNG requirements for a new category of medium developments (between ten and 49 dwellings, and where the site is less than one hectare, or sites between 0.5 and one hectare if no number is known).
Simplify the Small Sites Metric (SSM)
The proposal is to rebrand the SSM to the “low impact metric” and apply it to sites smaller than one hectare in size where no priority habitats are present. This would extend the rebranded SSM to apply to “medium” category developments, not just the minor category. The consultation also proposes amending the SSM trading rules, simplifying the habitat classifications by merging some habitat categories and improving competency requirements, as well as allowing garden biodiversity features to count toward the 10% gain. There is also a proposal for an online version of the SSM and the main metric tool for ease of use as both are currently in an excel format.
Relaxing requirements to prioritise on-site compensation
Changes to the off-site BNG rules to reduce cost and complexity. The consultation proposes relaxing the requirement to prioritise on-site over off-site compensation when applying the biodiversity gain hierarchy (for minor development only). There is a proposed review of the spatial risk multiplier for minor developments purchasing off-site units or using local nature recovery strategy areas alongside national character areas instead of local planning authority boundaries, this is to make unit sourcing cheaper.
Changes for brownfield developments
The consultation includes proposals relating to open mosaic habitats characterised by a mix of bare or sparsely vegetated areas and more densely vegetated patches.
The government published a consultation on implementing BNG for nationally significant infrastructure projects (NSIPs) on 28 May 2025. To read about this consultation in full, please click here.
The proposals set out above are elements that BPE have considered to be key proposals of the consultation and are not an exhaustive list of the proposals in the consultation.
If you would like further advice on the impact of the consultation on your development, or would like any practical advice on property matters please get in touch with Paul Engelbrecht on [email protected] or 01242 224433
