It is time to decide to "close... or open the door" to nuclear power, Trade Secretary Alan Johnson has said.
The government is asking industry and the public for ideas
He said the 2003 Energy White Paper "had rightly" focused on boosting renewable energy and energy efficiency, but left the door "ajar" on nuclear.
But, as a public consultation into UK future energy needs begins, he said it was time to take a decision on nuclear.
Critics say nuclear power is too expensive, is a terror threat and creates much radioactive waste.
Mr Johnson spoke out as it emerged that ministers had asked the Health and Safety Executive to look at the safety, cost and suitability of existing nuclear plants.
Environmental campaigners fear the HSE study is a prelude to an expansion of Britain's nuclear network.
They believe the HSE review, set to take 18 months, has been requested to save time if the government does give the go-ahead for new power stations.
Mr Johnson says he still has an open mind, but adds that it is "crucial" to consider how Britain will meet its energy needs in the next 50 or 60 years.
He said the HSE would also look into the viability of other ways of generating power, such as wind turbines, gas transport and storage and carbon capture and storage.
And as he launched a three-month public consultation on the issue, he said: "We need to look at the risks to security of supply, our climate change commitments and, to the long term, to make sure we take the necessary action. There is not a do-nothing option."
Mr Johnson said by 2020 coal and nuclear generating electricity plants producing 30% of UK electricity will have closed.
"Companies will need to decide how this capacity should be replaced. These are big investment decisions so the government needs to provide a clear framework," he said.
While renewable sources of energy would be an element towards filling that gap, he said the security of oil and gas supplies from overseas had to be considered, especially in the light of the recent dispute between Russia and Ukraine.
"If gas, as well as renewables, were to fill the gap, how comfortable will we be relying on imports for 80% of our supplies?" he asked.
Energy Minister Malcolm Wicks, who is leading the review, said people could do more to conserve power, adding that more than £740m of energy was "squandered" by domestic appliances and gadgets being left on stand-by rather than switched off.
But Norman Baker, the Liberal Democrats' environment spokesman, said: "This review is simply a retrospective way of justifying the prime minister's wish to build a new generation of nuclear power stations, something the earlier White Paper did not recommend."
Keith Taylor, the Green Party principal speaker, said nuclear power was "astronomically expensive", was "incredibly dangerous" and used fossil fuels at every stage in the process apart from fission itself.
Tony Juniper, executive director of Friends of the Earth, said: "We can tackle climate change and meet our energy needs by cutting waste, harnessing the power of renewables and using fossil fuels more efficiently."
The Engineering Employers Federation, which represents thousands of companies, said the government had to quickly decide on a coherent energy plan and had to consider all options, including nuclear power.
The Energy Saving Trust said there was a pressing need to solve the "escalating demand for energy" while still keeping the UK's carbon emission quotas to Kyoto Protocol targets.