Parliament's Public Accounts Committee has called Sizewell C "a terrible deal for the UK taxpayer". If construction costs rise to the top of the government's estimated range, the committee says consumers could pay £9.8 billion more during construction and a further £12 billion over the plant's 60 year operating life, all in real terms. That is £21.8 billion in total, by our calculation. Private investors would need to put in only £30 million more.
The report, published on 28 October, says "consumers and taxpayers shoulder significant financial risks, while private investors enjoy protected profits". It adds: "The UK must never be put in this position again." The committee, chaired by Sir Geoffrey Clifton-Brown, blames "successive governments' failure to deliver new nuclear" for leaving the UK with these terms.
The figures come from the move between two regulatory thresholds for construction costs, £40.5 billion and £47.7 billion. Consumers would pay more not only for the extra construction, the committee says, but for "the cost of the additional borrowing and payments to shareholders over a longer period". The £21.8 billion is a modelled scenario spread over decades, not a forecast of bills; the £30 million is the extra cash investors would put in.
Investors are still expected to do well. The committee says their annual returns are expected to be 12 to 13 per cent if costs stay low, falling only to between 10.8 and 11.4 per cent if costs reach the higher threshold. Overruns above the lower threshold are shared equally between investors and consumers, but the investors' main penalty is a cut of up to 1.6 percentage points in their return. The committee says this "breaks the rule that financial returns be proportionate to the risk". The National Audit Office concluded it is "not clear" whether the structure gives investors enough incentive to keep costs down.
The Department for Energy Security and Net Zero struck the deal in July 2025, when Ed Miliband was Energy Secretary. Until then the department held 90 per cent of Sizewell C Ltd. It now holds 44.9 per cent, which gives it "veto rights but does not give [it] control", even though the public provides most of the money. The government provides up to £37 billion of debt through the National Wealth Fund, with a further £5 billion from commercial lenders backed by guarantees from the French export credit agency. At least one government guarantee has a maximum value of £70 billion in nominal terms, payable if the project is discontinued or permanently shut down and Sizewell C Ltd is not at fault. That is a maximum exposure, not a forecast.
Control sits with a board on which private investors hold the majority. Nigel Cann, Sizewell C's chief executive, is its Accounting Officer, answerable to Parliament for public money. The committee warns that "a board dominated by private investors could direct the company in ways that conflict with the AO's personal responsibilities under Managing Public Money", and says it is "less confident than the Department" that government influence through the boards will always be enough. Jonathan Brearley, the department's permanent secretary, gave evidence on 8 June. Miatta Fahnbulleh has been Energy Secretary since 20 July 2026.
The department's own analysis assumes a fully public project would be delivered at the higher threshold. On that basis, private investors must deliver £4 billion of construction savings and finish two years sooner to justify what their returns cost consumers. The committee says it is uncertain whether they will, and that cheaper ways to improve delivery may have existed. The department said it used a competitive process and secured the EDF and private investment it wanted at a price it saw as acceptable. The committee says investors "clearly required a 'nuclear premium'", reflecting the UK's record in nuclear construction.
The construction risk is real. Sizewell C is expected to cost between £40.5 billion and £47.7 billion and to finish between 2039 and 2043. Its reactor design has been used five times before: in France, in Finland, twice in China and at Hinkley Point C in Somerset. The committee says "no comparable nuclear power station anywhere in the world has been delivered on time and on budget", and that projects using the design have had "delays of up to 14 years and substantial cost overruns". The department argues that repeating Hinkley Point C's design and applying its lessons will reduce the risk.
The department's economic case says Sizewell C could deliver up to £18 billion of net present social value, mainly by cutting electricity system costs by £2 billion a year compared with other low carbon options. That is a modelled estimate, not a return to the taxpayer. The NAO said the risk sharing "appears to have reduced the cost of financing the project". The company has a target for 70 per cent of construction spending to be in the UK, though much of the highest value reactor technology comes from France. Consumers will fund a decommissioning pot of £5.1 billion to £5.8 billion in nominal terms, with investment growth expected to cover the rest of an estimated £12 billion cost; if it falls short once the station has closed, taxpayers pay the difference.
The government plans to report publicly on the project once a year, while shareholders get six monthly updates verified by an independent technical adviser. The committee called annual reporting "totally inadequate given the project's level of risk". It recommends that Sizewell C Ltd and the department report to Parliament every six months on costs, schedule, milestones, risks to consumers and taxpayers, the expected effect on bills and forecast investor returns, with the underlying data published in machine readable form. It also wants Sizewell C Ltd to send the committee, within three months, the scenario analysis behind its cost thresholds and its current assessment of how likely each scenario is.