Lord May of Oxford, the outgoing president of the Royal Society, said that environmental campaigners risked holding back the fight against climate change with an absolutist approach that refused to consider nuclear power.

"I recognise there are huge problems with nuclear, but these have to be weighed against other problems," Lord May said. "This has to be recognised as a problem by what you might call a fundamentalist belief system.

"Fundamentalism doesn’t necessarily derive from a sacred text. There are also NGOs [non-governmental organisations] that are reluctant to weigh one problem against another, but have a subset of problems that are absolute and undiscussable."

He will go further in a valedictory speech today, linking such opposition to a resurgent fundamentalism, more often displayed by religious extremists, that threatens free scientific inquiry.

His warning came as Tony Blair announced to the CBI conference his long-awaited energy review, which will recommend next summer whether to start building new nuclear power stations in readiness for when the present nuclear plants are due to be decommissioned in about 2020.

Mr Blair was prevented from making his speech in the main conference hall by two Greenpeace demonstrators who climbed up an inside roof overlooking the stage. Instead Mr Blair spoke in improvised form in a crowded side meeting room.

The Prime Minister said that Britain and other countries would have to diversify into several sources of energy and predicted that the Kyoto Protocol governing carbon emissions, which expires in 2012, would be followed by a binding international agreement covering all leading economies.

"Energy prices have risen. Energy supply is under threat. Climate change is producing a sense of urgency," Mr Blair said. "The future is clean energy and nations will look to diversify out of energy dependence on one source."

In 15 years Britain would have decommissioned both coal and nuclear plants that between them accounted for 30 per cent of today’s electricity supply, he said. "Some of this will be replaced by renewables but not all of it can."

The CBI ordered an immediate review of its security after it was discovered that the two Greenpeace protesters, who posed as conference delegates, had paid for delegate passes through a bogus company, E-Lingo, before scaling girders to reach the roof. The pair, Huw Williams and Nyls Verhauelt, were later arrested.

Two legitimate passes were issued to Greenpeace delegates, although the campaign group was refused permission to erect an exhibition stand in the hall.

Malcolm Wicks, the Energy Minister, who will head the Government’s review, said that it would consider ways of speeding up any planning inquiries should new nuclear power stations be proposed. These would require private investment but would need "some special relationship between the market and the state in this area".

The review would also look at renewable energy, coal, gas and new technologies, plus transport systems and energy efficiency, Mr Wicks said. Its aim was to identify clean, reliable, affordable energy supplies for the long term.

Charles Kennedy, the Liberal Democrat leader, protested at the cost of disposing of nuclear waste and the decommissioning of plants, saying that it would amount to a "nuclear tax". The money would be better spent investing in renewable energy and encouraging energy economy, he said.

The Conservatives welcomed the review but were non-committal on nuclear power, although it is supported by a number of party figures.

Business organisations took a similar stance, saying that the Government must develop a clear policy and secure energy supplies but without taking sides over nuclear power.

Sir Digby Jones, Director-General of the CBI, would say only: "Potential investors in new power generation plant require a clear and stable framework from government in which to plan. We now need to see a full and informed debate that engages the whole nation, and leads to a clear conclusion — whatever that is."

But environmental groups urged ministers to reject the nuclear option. Tony Juniper, of Friends of the Earth, said: "Nuclear power is dangerous, expensive and unnecessary."

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