Campaigners say fresh funding fears have cast doubt on the viability of Suffolk’s new nuclear power station.
The Theberton and Eastbridge Action Group on Sizewell C (TEAGS) said a letter from the nuclear industry urging government to support a new financing model for electricity infrastructure exposed the vulnerability of new projects.
TEAGS' Alison Downes said the Nuclear Industry Association submissions to the Chancellor highlighted growing worries the Treasury may ditch plans for a new funding model, on which EDF Energy's business case for Sizewell C depends.
The NIA's letter warns it will be impossible to replace the nation's ageing nuclear power stations and achieve carbon net zero targets without the right investment policy.
It says there is an "urgent need" for a new financing mechanism to ensure "investor confidence, reduce the cost of capital and provide very significant value to the consumer."
The letter goes onto say timing is "critical" - as the business case for Sizewell C depends on the timely transfer of operations from Hinkley Point C; EDF's sister project in Somerset.
It calls on government to respond to consultation on the 'Regulated Asset Base' model of funding, which was opened last year.
RAB grants companies rights to charge a fixed price to consumers in exchange for providing the infrastructure.
MORE: Could escalating costs mean 'game over' for nuclear power and Sizewell C?EDF said RAB could lead to lower financing costs and "significant savings" for consumers.
However,opponents say RAB would expose bill-payers to huge costs.
Paul Dorfman, founder of the Nuclear Consulting Group, said new nuclear projects had experienced "vast cost and time over-runs".
"Under RAB, the plan is for the burden of risk to pass to hard-press UK consumers and taxpayers," he added.
The RAB model, which has also been termed a "Sizewell surcharge", sparked major opposition when consultation launched last year. More than 46,000 people have signed a petition opposing the plans.
Chris Wilson of Together Against Sizewell C said at the time of the petition that without massive subsidies, nuclear projects will "crash and burn".
Mrs Downes said the industry was right to worry that the Treasury may ditch RAB.
"Based on its other projects, it will be impossible for EDF to accurately predict how much Sizewell C will cost and how long it will take to build," she added.
"EDF has made it clear that RAB is essential for Sizewell C to proceed, but it will be too expensive, slow to deliver and is not the answer to our climate emergency.
"Any funds spent building Sizewell C would suck vital resources away from cheaper, faster green energy, energy efficiency measures and innovation in new technologies."
The Treasury declined to comment.
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