Sir Alec Broers, the president of the Royal Academy of Engineering, said that government plans to generate 20 per cent of electricity from renewable sources by 2020 were unrealistic and investment in nuclear power was critical if shortages were to be avoided.

All but one of the nuclear plants that now generate almost a quarter of Britain’s electricity are due to close in the next two decades, and ministers have refused to make a commitment to building replacements.

The recent Energy White Paper instead set ambitious targets for renewable power, such as wind and tidal energy, and plans to meet remaining electricity needs from fossil fuels.

This policy made overoptimistic assumptions about the potential and cost of renewables, and would do little to cut emissions of greenhouse gases, Sir Alec said.

While the Government was right to invest in wind power, it would be a huge and misguided gamble to ignore nuclear power as an important element of the energy mix.

Sir Alec’s fears, which he voiced in an interview with The Times, add to growing concern about the security of Britain’s energy supply, an issue that has risen sharply on the political agenda after the blackout that struck the United States and Canada last week.

Energy experts said on Friday that similar power cuts could happen here as soon as next winter, and Brian Wilson, a former Energy Minister, said that electricity prices would have to rise to improve capacity.

Reports from the Royal Academy of Engineers and the Institution of Civil Engineers have told ministers that they will have to approve new nuclear power stations to guarantee future supplies.

Sir David King, the Government’s Chief Scientific Adviser, has made the same recommendation.

Roger Higman, of Friends of the Earth, disputed the need for new nuclear power stations, however, saying that there were better ways of reducing greenhouse emissions.

“Nuclear power is expensive, dirty and unreliable,” he said. “Last week France was desperately trying to hose down its nuclear plants to keep them operational in the heatwave, and the closure for safety reasons of ten nuclear plants in the US was instrumental in the crash of their electricity system.

“The problem with listening to engineers on this issue is that they see one part of the problem, but not the broader environmental issues that are at stake.”

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