75 GW of nuclear power - enough to provide 86% of UK electricity - could be brought on line by 2050.
Up to 50 nuclear power stations could be built under plans being looked at by the government. The remarkable figure - 10 times the number the government is openly discussing - is revealed in documents submitted to DECC - the Department of Energy and Climate Change - by one of its own advisory bodies.
The documents are likely to raise questions as to what extent the government's energy policy is weighted in favour of nuclear and away from renewables such as wind turbines.
It comes as Brussels begins an investigation into whether Britain is providing up to £17bn of potentially illegal public guarantees for the first nuclear power plant in a generation, Hinkley Point C in Somerset, which aims to provide 7% of the country's electricity.
In a submission to a consultation on geological waste disposal, the Committee on Radioactive Waste Management has said an upper limit of 75GW (gigawatts) of nuclear power is "being examined" by DECC in London.
The current programme announced by ministers is to build 12 reactors to supply 16 GW at five sites. The higher figure equates to more than 50 new large-scale modern reactors.
The committee has been given the task of assessing the number of disposal facilities that might be required for the waste that will be produced by new nuclear power stations. It notes that the 16-gigawatt programme is only the "first tranche" and is "substantially below the 75 gigawatts upper limit being examined" by DECC.
The upper limit echoes a scenario outlined by the energy department in a 2011 report, outlining its vision for a low-carbon future. It suggested 75 GW of nuclear power - enough to provide 86% of UK electricity - could be brought on line by 2050.
"Nuclear energy is vital for our energy security and we want it to be part of the energy mix in the future, alongside renewables and clean coal and gas", a department spokeswoman said.
"It's important to model potential scenarios to plan for our future energy needs, but we haven't set any targets for the amount of new nuclear to be developed."
But Dr David Lowry, an environmental policy consultant and nuclear specialist, said the 75-GW scenario was a "nuclear fantasia at it worst", and failed to explain how huge amounts of radioactive waste generated by the plants would be stored.
Jamie Doward writes for The Observer, part of the Guardian media group, where this article was first published under the title Fifty new nuclear plants could be goal in official energy plans.
