20th July 2026
Biodiversity Net Gain (BNG) is now embedded within terrestrial planning in England, requiring most developments to deliver measurable biodiversity improvements compared to the pre-development baseline. While the terrestrial system – which includes intertidal areas extending to the mean low water mark – is now operational, attention is increasingly turning towards the marine environment and the development of Marine Net Gain (MNG) policies.
This blog looks at the progress to date in relation to the development of MNG with a view to providing an update to ISEP members.
The UK Government’s Environmental Improvement Plan (EIP) and commitments under the Environment Act 2021 recognises that marine ecosystems are under increasing pressure from development, climate change, pollution and habitat loss.
The Government has set targets for 48% of designated features in Marine Protected Areas (MPAs) to be in a favourable condition by the end of January 2028, and 70% by 2042. MNG may be an important contributor to achieving this long-term target.
As MNG policy continues to develop, two broad approaches are currently being explored, each addressing different challenges within the marine environment.
The first is Natural England’s Marine Net Gain Assessment Framework, developed through a series of pilot projects and assessment studies. This approach focuses on creating a robust scientific and regulatory framework capable of measuring biodiversity losses and gains associated with individual developments. The emphasis is on transparency, accountability and ensuring that gains are measurable, verifiable and additional to existing conservation commitments.
The second is the Strategic Marine Net Gain (SMNG) approach proposed through the Offshore Wind Evidence and Change Programme’s Marine Net Gain Task and Finish Group. Rather than concentrating on individual projects, this approach seeks to direct investment towards strategic marine restoration priorities identified at regional and national scales. These may include the recovery of MPAs, delivery of Marine Plan objectives, and progress towards Good Environmental Status under the Marine Strategy Framework Directive.
While both approaches aim to improve the marine environment, they differ significantly in their philosophy.
In summary, the Natural England framework asks:
How can we measure the impacts of a development and ensure biodiversity gains exceed losses?
In summary, the Strategic Marine Net Gain framework asks:
How can development investment be directed towards the places and habitats where marine nature recovery is most needed?
The distinction is important. A project-led system may risk generating numerous small, disconnected enhancement projects that may satisfy regulatory requirements but fail to deliver ecosystem-scale recovery. A strategic approach seeks to aggregate investment and direct funding towards larger restoration programmes capable of delivering meaningful and connected ecological outcomes.
Below, larger restoration initiatives illustrate the types of interventions that could underpin MNG:
- seagrass recovery projects in the Solent, Plymouth Sound and Falmouth Bay;
- native oyster reef programmes including the Wild Oysters Project; and
- large-scale saltmarsh creation schemes such as that at Steart Marshes.
More recently, offshore wind compensation policy has begun to adopt strategic, ecosystem-scale approaches, directing investment towards priority restoration programmes.
Perhaps the most effective future system will combine the strengths of both models. Whatever the approach, a robust assessment framework will be required to provide the scientific basis for calculating losses and gains.
Such a hybrid model could perhaps provide one of the first genuinely sustainable funding mechanisms for marine nature recovery in England. Instead of relying on grants, charities and short-term project funding, restoration initiatives could receive long-term investment linked to development activity. The hope is that this could help scale up marine habitat restoration programmes, support monitoring and adaptive management, and deliver measurable biodiversity improvements across MPA networks and beyond.
MNG is clearly still evolving. The last formal Central government announcement was on 9 December 2023 – the Defra Government Response to MNG consultation – and posed the question ‘How does Marine Net Gain fit within the wider environmental ambitions for this Government?’.
Assuming the current Government is supportive, important challenges remain. Questions on whether enhancements within MPAs can be considered ‘additional’ to existing statutory conservation obligations, and how to set up effective governance, monitoring, spatial prioritisation and long-term stewardship, must be resolved if MNG is to secure the confidence of both developers and conservation organisations.
Another key question is how will MNG learn from, and align with, the existing terrestrial BNG regime, particularly in the intertidal environment. The Lead Environmental Regulator will need to be decided upon, alongside an approach which is streamlined and proportionate, aligning with the findings of the Corry review.
Despite the complexity, the direction of travel is clear and if implemented effectively, it is hoped MNG will improve marine environments and potentially provide a mechanism for directing private investment into marine nature recovery, helping to deliver healthier seas while supporting sustainable development.
For organisations already engaged in restoration projects, the emerging frameworks present a potential opportunity to position existing initiatives within a future market for biodiversity enhancement. For others, now may be the time to start identifying the habitats, partnerships and projects that could contribute to the next generation of marine conservation.
MNG may still be in development, but its potential to unlock long-term, sustainable funding for marine nature recovery is exciting and something that organisations in the marine sector could use to achieve results for nature alongside socio-economic growth.
