The High Court has refused permission for a judicial review of the government’s decision not to amend the Sizewell C development consent order (DCO) to reflect potential future flood defences. Justice Mould ruled that the application brought by campaign group Together Against Sizewell C (TASC) was “totally without merit”, confirming that it was open to the secretary of state for energy security and net zero not to exercise his powers to vary or revoke the DCO at this stage.
The DCO for the twin‑reactor nuclear project on the Suffolk coast was granted in 2022, covering construction and operation of the main plant and associated works. TASC wrote to the secretary of state in March 2025 seeking a variation or revocation on the grounds that the approved scheme might not be resilient to extreme sea level rise scenarios, and subsequently issued legal proceedings when the request was rejected.
Central to the challenge was a 2024 Office for Nuclear Regulation (ONR) document which, according to TASC, indicated that additional overland flood barriers could be required in a maximum sea level rise case. The campaigners said the ONR material referenced two potential sea defences of around 10m crest level, one approximately 500m long and another up to 1km, which they argued had not been assessed under the Conservation of Habitats and Species Regulations 2017 when the DCO was examined.
TASC further relied on an internal EDF disclosure which it said showed the developer had been aware since 2017 that the consented platform level might be too low under a credible worst‑case sea level rise. The group alleged that EDF had kept the option of additional sea defences “secret” during the 2020 DCO application process, preventing public scrutiny of those structures and of alternatives such as increasing the platform height at design stage.
In his decision, Justice Mould found there was “fundamental uncertainty” as to whether the additional flood protection works identified in the ONR material would ever be required. He accepted that the regulatory framework allows for staged assessment of environmental and safety impacts, and concluded that the secretary of state was entitled to leave any further assessment and consenting of such defences to a later stage rather than reopening the DCO now.
TASC said it was “extremely disappointed” by the ruling and described it as “immoral” to proceed with a nuclear project it considers insufficiently resilient to extreme sea level rise. The group warned that “future generations” would have to “pick up the pieces from ill-thought out decisions made today” and reiterated its view that Sizewell C represents a “questionable climate change solution” with “hidden risks” that have not been fully scrutinised.
The campaigners argue that the Suffolk coastline is already subject to significant erosion and is highly exposed to future sea level rise, increasing the importance of robust primary and secondary flood protection. Sizewell C is designed to sit on a platform at 7.3m above ordnance datum (AOD), but TASC maintains that this may not be sufficient under upper‑bound climate projections and that raising the platform could be less environmentally damaging than retrofitting large overland barriers.
Recent analysis reported by New Civil Engineer, using Climate Central data, indicates that a substantial portion of the Sizewell C site could fall below the annual flood level by 2050. While this does not directly alter the legal position on the DCO, it is likely to keep flood resilience and coastal defence strategy under close scrutiny as the project moves through detailed design, regulatory hold points and construction phases.
Following the High Court’s refusal of permission, TASC has said it will consult its legal team on possible next steps. For the project team and supply chain, the ruling removes an immediate legal risk to the DCO but leaves ongoing regulatory engagement on flood risk, coastal processes and long‑term resilience as a critical factor for programme delivery and future consenting of any additional defences.
