Former energy secretary Sir Ed Davey has said building a new nuclear power station at Sizewell is "too expensive".
Instead the new Liberal Democrat leader argues the government should invest more in renewable energy to help boost the economy.
"The economic case for nuclear power is not there any more," said Sir Ed.
Energy firm EDF, which is behind the £20bn proposals, said the plant on the Suffolk coast would deliver low-carbon electricity.
Sir Ed, energy minister during the 2010-15 coalition government, approved plans for a new nuclear plant at Hinkley Point in 2013 and secured Chinese investment for the site on the Somerset coast.
At the time he described it as "a milestone on the road to decarbonisation".
But now he said: "The cost of offshore wind energy has fallen dramatically and renewables are cheaper than nuclear.
"We can build them locally, we don't need Chinese investment. Let's tap into this energy source that we control, that is clean, green and that creates green jobs in the region."
Next week sees the deadline for interested parties to register their interest in the planning inquiry into Sizewell C.
It is expected to be about 18 months before a final planning decision is made and the plant would then take 10 years to build.
A spokesman for EDF said it would be a "near identical copy" of Hinkley Point C which would cut out "first-of-a-kind construction costs".
"This makes it cheaper to build and finance, and cost-competitive with other low-carbon technologies," she said.
The French-owned energy firm said it would create about 7,500 jobs at the peak of construction.
Suffolk County Council and East Suffolk Council have expressed concerns about the impact on tourism and of increased traffic construction traffic.
EDF said it was sensitive to people's concerns and was working to reduce the impact.
A spokesman for the government's Department for Business, Energy & Industrial Strategy said nuclear energy was "an important part of our energy mix and we are committed to protecting the range of high quality jobs the sector supports".
"All nuclear projects in the UK are conducted under robust and independent regulation to ensure that the UK's interests are protected.
"We regularly engage with all developers on their projects and are considering a range of financing solutions."
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