Government plans for nuclear power risk handing control of the UK's climate and energy policies to France, according to four senior environmentalists.
Energy giant EDF and reactor builder Areva, big players in the UK's plans, are largely French government-owned.
Jonathan Porritt, Tom Burke, Charles Secrett and Tony Juniper say the firms are landing UK citizens with all the financial risks of nuclear new build.
They have told Prime Minister David Cameron he is being badly advised.
The four - all former directors of Friends of the Earth (FoE) UK - say that the current policy to start building at least eight new reactors over the next decade cannot withstand the "intense scrutiny" it is coming under in the wake of the Fukushima disaster in Japan.
"There is now a growing risk of policy failure," they write in their letter to the prime minister.
Mr Cameron recently signed an agreement with French President Nicolas Sarkozy to boost nuclear co-operation.
"Our analysis shows that building new nukes will be a massive rip-off for the the British taxpayer," said Mr Secrett.
"How on Earth can the prime minister justify paying billions of pounds of subsidy to French power companies when the chancellor is slashing welfare budgets for poor people in Britain and there are a million young people unemployed?"