The Solent Forum

Working in partnership for the future

Biodiversity & Marine Net Gain

Biodiversity Net Gain (BNG) is an approach to development that leaves biodiversity in a better state than before. Where a development has an impact on biodiversity it encourages developers to provide an increase in appropriate natural habitat and ecological features over and above that being affected. It is hoped that the current loss of biodiversity through development will be halted and ecological networks can be restored. It will apply from January 2024 (current agreed date) for developments in the Town and Country Planning Act 1990 and to small sites from April 2024.

In England, BNG was mandated from 12 February 2024 under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021). The Act states development must achieve at least a 10% net gain in value for biodiversity – a requirement that habitats for wildlife must be left in a measurably better state than before the development. Developers must submit a ‘biodiversity net gain plan’ alongside usual planning application documents. The local authority must assess whether the 10% net gain requirement is met in order to approve it. If net gain is not achievable on-site, the plan will need to include off-site habitat enhancements, in line with the mitigation hierarchy; the local authority must be satisfied that this is secured through a planning obligation or conservation covenant. Natural England have published Biodiversity Net Gain - Summary of Intertidal Differences (JP056).This states that for protected sites that contain intertidal habitats, BNG units can be delivered on both designated and non-designated features of the site where such features are on or comprise intertidal habitats.

There is a separate system that applies to marine development (Marine Net Gain (MNG)) which is currently under development.

Marine Net Gain

UK Government published its response to the public consultation on the principles of Marine Net Gain in 2023, clarifying it will only apply to developments below the mean low water mark in England. Key next steps in its development will include the creation of an assessment framework for Marine Net Gain delivery, implementation of proof-of-concept projects, development of detailed supporting policy, a full cost-benefit-analysis, and determination of legislative powers.

Many marine developments will however ultimately land onshore and will also have terrestrial and intertidal elements, they may be subject to both BNG and MNG in the future. Defra have committed to ensuring that MNG is as coherent and consistent with land-based BNG as possible. In 2022 Defra consulted on the principles of marine net gain.

There is a broad call for meaningful and strategic aspirations for the marine and intertidal space rather than just a metric. In 2021, ABPmer was commissioned by the Offshore Wind Energy and Change (OWEC) Marine Net Gain Task & Finish Group, which is working closely with Defra’s Offshore Wind Enabling Actions Programme (OWEAP), to conduct a survey amongst key stakeholders and develop recommendations for strategic targets for Marine Net. This work has led to an assumptions paper that describes a proposed approach looking at where intertidal/marine are failing and where there is a need to foster recovery.


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