Well before anyone has seen the details of today's nuclear white paper, the battle lines have been drawn with just about everyone involved in the environment and energy debates taking sides. Last night, in a rare show of near-unanimity, three of the four London mayoral candidates, including Ken Livingstone, Brian Paddick and Sian Berry, came out strongly against nuclear.

Boris Johnson pointedly did not sign the letter which read: "As Mayoral candidates for London we believe that we can meet our city's energy needs through becoming much more efficient with our energy use, local energy generation and exploiting our renewable resources."

When the announcement to reconsider nuclear power was made two years ago, some environmentalists said they were in favour of the controversial energy source because nuclear power seemed to offer a stop-gap solution until renewables came on stream. But last night, there was almost total unanimity among greens that nuclear was not the answer.

However, almost all the leaders of the UK's major energy and engineering institutions have come out strongly in favour. Andrew Furlong, head of policy at the Institution of Chemical Engineers, yesterday said: "25 years ago you would have found me vigorously protesting against Sizewell B - but times have changed. Any sound scientific assessment of the energy and climate change challenges facing humanity reveals that it is nigh-on impossible to maintain existing living standards and keep carbon emissions within tolerable limits without retaining a nuclear power generation component".

He was was joined by the Royal Academy of Engineering, the institutes of marine engineering, mechanical engineers, physics, structural engineers, civil engineers, the UK energy research institute, the British computer society and the Dalton nuclear institute at the University of Manchester.

But the green lobby responded saying these were largely made up of vested interests, who could expect to benefit from the spin-offs of a new generation of nuclear power. Stephen Hale, director of Green Alliance, said: "The government's obsession with nuclear power overlooks critical facts. First, nuclear electricity will not bring us security by eliminating our need for foreign gas and oil, as 86% of our gas and oil is not used for electricity.

"Second, nuclear power causes an expensive and dangerous waste legacy that we still do not know how to manage and which is already costing the British public £2.8bn per year. The government is wasting precious time and money on a technology that cannot deliver. "The promise of nuclear power has always proved illusory. We can't afford to wait for nuclear to fail again."

Friends of the Earth director, Tony Juniper, spoke for many: "The decision to encourage the construction of new nuclear stations in the UK is both irrational and unfortunate. "It is irrational because the economics do not stack up and because renewables and energy efficiency could meet our needs more quickly and sustainably.

"It is unfortunate because the nuclear option will limit our ability to lead in the exciting and fast growing new markets for modern energy sources. And that is bad news for the UK economy and jobs".

The Royal Society, effectively the UK academy of science, however, was remarkably guarded in the run-up to today's announcement. "It is good news that decisions are finally being made on how we will meet future energy needs as it is likely that any new power generation capacity will take at least 10 years before it provides any energy.

"Regarding the option of nuclear power, there remain key questions on safety and security that need to be openly addressed. The government needs to maintain an open discussion with the public, that is informed by the best science and engineering, on issues such as the safe disposal of nuclear waste."

(By John Vidal, The Guardian, 10/01/2008)