"Throw away the emission targets and there is no problem. But keep them and the nuclear option has to be the way," John Loughead, director of the UK Energy Research Centre, told a news conference presenting a report on the future of energy supply.

He said nuclear power was not the only option but part of a basket including coal, oil, gas, wind, waves, solar, and biomass as well as increasing energy efficiency and the politically unpalatable task of making people change the way they live.

But given the time frame and the need to cut emissions of gases like carbon dioxide from burning fossil fuels, then nuclear had to be the answer.

"We see no way of supplying the energy needs without maintaining the nuclear capacity," Loughead said, noting that the growth of renewables was only gradual and it would take far longer than a decade to change peoples' lifestyles.

But Friends of the Earth chief Tony Juniper rejected the conclusions.

"We reject nuclear new build. If there is one lesson we have learned from the past it is that nuclear has always cost far more than its proponents have claimed," he said. "If we take the nuclear route it is likely to be the most expensive.

"We have an answer now. Energy efficiency is available and affordable," he added.

The report is the result of a two-day meeting last month in London of 150 scientists, economists, technical experts and sociologists.

It is a intended to fuel the debate on the future of the country's energy policy in the face of global warming, with the government likely to have to take a decision within a year on whether to renew the decades-old 11 nuclear power stations.

It said fossil fuels would remain Britain's main energy source for the next 50 years and renewables would play a rising role but need continued government support, as would moves to improve energy efficiency -- particularly in buildings.