Why Stop Sizewell C? (updated July 2025)

Overview: Sizewell C is intended to be two ‘EPR’ nuclear reactors on the Suffolk Heritage Coast at an expected cost of at least £38bn. Planning consent was controversially granted in July 2022  and the Conservative government became a partner in Sizewell C in November 2022, investing £2.5bn. No Final Investment Decision (FID) was reached before the 2024 election, and Labour invested a further £1.2bn, then committed £14.2bn in the June 2025 Spending Review, making a total of almost £18bn. A Final Investment Decision was made on 22 July 2025. Below is a summary of the reasons we oppose Sizewell C

Finances

• Sizewell C is expensive: the new “baseline” cost is £38bn [2024, real], a staggering increase from the only previously published cost of “circa £20 billion” in May 2020 (p5). An Office for Nuclear Regulation Inspector told Stop Sizewell C it is “an expensive site to develop” (see Site Suitability). There is no clarity about how much electricity would cost consumers, making external scrutiny of Value for Money against other electricity sources very difficult. 
• Who will pay for it? At FID, the UK government has a 44.9% stake, EDF has 12.5%, Centrica 15%, Canadian Pension Fund La Caisse 20% and Amber Infrastructure 7.6%. 
• Risk borne by households: Sizewell C will use the Regulated Asset Base funding model, which loads construction risk onto households via a “tax” on energy bills during the lengthy construction period to give investors an immediate return. Ministers say this levy will be £1/month for an average household, but only after the government has “recycled” the revenue received from its own share (44.9%). In January 2024 Citizens Advice told Ministers “at Sizewell C.. the scope for material cost and time overruns is very significant. Consumers need to be protected from those risks. They have no way to manage them…”
• Track record of the EPR reactors. In its latest update of January 2024, Hinkley Point C’s cost is up to £35bn[2015], £17bn more than its £18bn budget – £46bn in today’s money. Following the refusal of China General Nuclear to pay more, France has said it wants the UK government to contribute to completing Hinkley C. Olkiluoto in Finland was 14 years late. Flamanville in France was at least 12 years late and has been experiencing problems in start up. Sizewell C claims Sizewell C will be cheaper, benefiting from being a replica of Hinkley, however it is not possible to replicate the site. To read more on this subject click here.
• Sizewell C will divert resources and investment away from renewable and net zero projects. 

Technical concerns with the EPR reactor

• Only three EPR reactors are in commercial operation. Taishan 1 in China closed for over a year with fuel failure early in its life and was offline again from February to November 2023. EDF framed Taishan’s fuel failure as about the robustness of fuel assemblies, but French regulators still demand design changes at Flamanville to limit core vibration (p6). After extended testing Olkiluoto 3 entered commercial operation in April 2023 but experienced two unexpected outages in November 2023 and its annual outage in early 2024 took five weeks longer than planned.
• Unlike the UK, France will not build any more EPR reactors. Former EDF CEO Henri Proglio said in December 2022: “The EPR is too complicated, almost unbuildable.” France instead intends to build six reactors of a simplified design called the EPR2, the first at Penly (p6). 

Contribution to energy security and addressing climate change

• Sizewell C will be slow, taking at least 10-12 years to build, so cannot generate any power until after the Labour government’s target date to decarbonise the UK’s electricity of 2030. They will therefore have to install some other form of electricity generation – such as cheaper, quicker renewables – to meet this target.  Sizewell C will not give a target completion date beyond mid-late 2030s, but under the terms of the Regulated Asset Base we know that the lower time regulatory threshold is end of 2039 and the higher threshold is 2043.
• Is Sizewell C a priority for France? Only EDF can build Sizewell C (even if not on time and budget, as it is their technology), and this places the project in competition with France’s own plans to build six EPR2 reactors. French Finance Minister Bruno Le Maire has stated EDF’s priorities should lie in France and the French Cour des Comptes expressed concern about this too in January 2025.
• It’s not needed. A PQ on the relative costs to consumers of an electricity system including additional nuclear or reliant on renewables alone shows DESNZ ‘did not look at a renewable only scenario …as this cannot ensure security of supply’. However many energy scenarios, eg by Oxford University’s Smith School, UCL, LUT (Finland) and Energy Systems Catapult (for Good Energy) affordably and quickly reach net zero without any new nuclear power beyond Hinkley C. Significantly, the government’s current Power Sector Model – the Dynamic Dispatch Model – which was used for the Sizewell C Full Business Case,  cannot model longer-duration storage (source: correspondence with DESNZ) and is being replaced.

Contribution to Economic Development and Levelling Up

• Sizewell C would not help the UK level up. A study by Development Economics found that five of the seven remaining “potential” sites in the nuclear National Policy Statement would likely benefit more.
• Sizewell C will only create 900 long term jobs in Suffolk; at £38 billion this would be £42m per job. For this sum, the UK could buy much more renewable energy and finance a mass energy efficiency programme which would create tens of thousands of sustainable jobs.
• Sizewell C will damage the Suffolk local economy. Research by the Suffolk Coast Destination Management Organisation – and  by Sizewell C – show that visitors will stay away, losing the tourism industry up to £40 million a year, at an estimated cost of 400 jobs. Sizewell C admits 725 ‘local’ staff would be recruited from existing businesses. 

Site (un)Suitability

• The RSPB said wildlife will be damaged during Sizewell C’s construction. It was also opposed by the Suffolk Wildlife Trust. The site is surrounded by protected wildlife habitats and adjoins internationally famous Minsmere. Some of Sizewell Marshes SSSI will be built on. The site is wholly within the Suffolk Coast & Heaths Area of Outstanding Natural Beauty (AONB); construction would cut the AONB in half.
• Water: the Planning Inspectorate was unable to recommend Sizewell C be granted Planning Consent due to the lack of an identified long term supply of potable water. Sizewell C needs 4 million litres/day during construction, and 2 million litres/day during operation. A desalination plant – initially rejected on environmental grounds – was approved for the construction period, but no long term source has as yet been assessed. Suffolk is one of the driest parts of the UK.
• The site is more complex and harder to access than Hinkley Point C. The platform will require a 60 metre cutoff wall so it can be dewatered, existing soil swapped for more suitable material, and huge sea defences, making it (according to a ONR Inspector) “expensive to develop”.
• Sizewell C’s case for coastal stability at Sizewell, despite serious erosion on the coast close by, depends on the presence of two offshore banks to reduce the power of waves on the Sizewell foreshore, but these banks have shifted in past decades. Cefas stated “it is generally only possible to predict detailed changes to the coastline over the next 10 years”. Unexpected erosion of the existing Sizewell sacrificial dune has occurred in the past 12 months. Sea defence plans are not yet finalised.
• Nuclear waste would have to remain on the coastal site until the middle of next century. The dates to which the site would need protection from sea level rise are disputed.
• Suffolk has considerably less infrastructure (the un-dualled A12 compared to the M5) and a smaller local workforce than Somerset where Hinkley C is under construction. 76% of the construction workers (6,000 out of 7,900) would be required to relocate from outside the area.