It was not the kind of outburst Professor Sir David King had expected when he became chief scientific adviser to the government. But he was, after all, dealing with John “Punchy” Prescott.

It was 2003 and Prescott thought he and the other ministers overseeing a new energy white paper had finally reached agreement to rule out nuclear options and instead to recommend concentration on renewables and energy efficiency.

“That was when I put my hand up,” King said last week, “and told him I still did not believe we could cut CO2 without nuclear power. Nor would I pretend I had changed my mind.”

King claimed that what happened next was shocking. Prescott “went ballistic”, shouting about collective responsibility and thumping the table. “I wondered if I was going to get punched,” King recalled.

He was saved by Margaret Beckett, who was environment secretary at the time. She told Prescott that the professor was simply doing his job of being an independent voice and not another cabinet clone.

A year later, King was surprised to get an invitation to visit the deputy prime minister. “I went to see him and he apologised, saying I had been right about nuclear after all. He had simply been too worried about the public reaction to supporting nuclear to agree with me.”

From which you may gather that King, who stood down from government on New Year’s Eve, sees himself as the outsider who fights received wisdom and is proved right in the end.

We met in the temporary offices of his new environment research institute in Oxford the day before the government announced its backing for new nuclear power stations. “I would like to think I played a large part in bringing about the new approach,” he said.

Prescott was, however, only his second most important conversion to the cause. “When I became chief scientist in 2000 Tony Blair was still very cautious about nuclear power. He did not even have an adequate understanding of climate change until 2002. For those first two years I was battling against the odds.”

King had arrived in office in 2000 determined that climate change, which he saw as the biggest threat to humanity, would be his great central issue. “Britain’s CO2 emissions were steadily rising despite our promises to reduce them, and the closure of ageing nuclear power stations and replacement with gas and coal was the main reason for that. That had to stop.”

In King’s view, Labour might never have listened to him but for the epidemic of foot and mouth disease (FMD) in 2001, which turned his office of science and technology from a government backwater into a centre of influence. “The outbreak of foot and mouth turned out to be crucially important,” he admitted.

Unimpressed by Whitehall’s efforts to stem the epidemic, he called in mathematical model-lers, who found it was out of control. He convinced Blair that it could be got under control within days by a draconian policy of mass slaughter, which brought the sight of millions of burning animal carcasses to tele-vision screens across the nation.

“It looked terrible,” he recalled, “but almost immediately the epidemic began slowing down. It showed the government what science could do. I could never have had such power in government if FMD had not happened.”

King was quick to capitalise on his new-found influence. In 2002 he “engineered” the opportunity to give the Zuckerman lecture for the British Association for the Advancement of Science, choosing climate change as his topic. Then he delivered the same lecture to Blair and the cabinet, both in person and on paper. “For Blair that was a turning point,” he said. “It was when he read that lecture that he realised that we had to do something about climate change.”

Was King being immodest or was Blair really so ignorant? Labour had, after all, been parroting the rhetoric of climate change and reducing greenhouse gas emissions for nearly a decade. “I think the point is that Blair had not understood the urgency,” King said. “He knew about climate change but until then it had just been another political problem.”

This illustrates his other great campaigning issue: the absence of scientific understanding among policymakers and the lobbyists who influence them.

“We have an education system where kids choose whether to study science as young as 12, and now we have a society where a lot of people do not understand what science is and what it can do. There are a lot of people in politics and the civil service who are from that background. It is a huge weakness,” he said. “The absence of scientific understanding often leads to superficial decision-making. The 2003 energy white paper was a good example of that. I would not like publicly to call it amateurish but it did not tackle the problem in a realistic way.”

King found convincing the Sir Humphreys of the value of science so difficult that he persuaded Blair to create the posts of chief scientist in eight government departments, with those appointed having direct access to ministers and permanent secretaries.

“It has made a big difference but not enough,” he said, singling out the Home Office and the Department for Culture, Media and Sport (DCMS) as still hampered by science vacuums. “The DCMS oversees institutions like the Science Museum and Natural History Museum, which spend tens of millions on science research, but the DCMS has no way of measuring how well it is being spent.”

King’s power has won him enemies. The civil servants tackling foot and mouth in 2001 remember with bitterness how he ripped up their carefully drawn plans for dealing with a new outbreak. More recently his rejection of the findings of a decade-long study on links between badgers and bovine tuberculosis brought a stinging rebuke from Nature, the scientific journal. It said: “The mishandling of the issue by David King is an example to governments of how not to deal with such advice.”

Others charge him with arrogance. Richard Horton, editor of The Lancet, recently accused him of “taking his faith in science into the realms of totalitar-ian paranoia” after he had criticised the media’s “scientifically uninformed” coverage of controversies over genetically modified crops and the measles, mumps and rubella vaccine.

It is partly with the aim of tackling the “scientific deficit” in such circles that King has just started work as director of the new Smith School of Enterprise and the Environment at Oxford University.

“A lot of this country’s future leaders come here to do courses like PPE [philosophy, politics and economics]. In the past that has largely excluded science but in future they will be able to take courses here that will help them see why science matters.”

King has also co-written a book, The Hot Topic (Blooms-bury, £9.99), a layman’s guide to climate change, which comes out this month. Freed from the shackles of government and the risk of being thumped by the deputy prime minister, he is keeping himself in the public eye in other ways too. Recently he told a young female questioner in a public lecture that the best thing women could do for the climate was stop admiring men who drive gas-guzzling sports cars.

What makes him so outspoken when he could be relax-ing? For King it’s the belief that humanity is now in deadly danger from climate change. The 1,000 billion tonnes of CO2 already released into the air by humans since the industrial revolution, and the 42 billion tonnes added to that each year, mean we are locked into a temperature rise of about 2C already.

“The scientific advice has been that we should prevent the world from warming by more than 2C,” he said. “This is the target adopted by the European Union but the very serious problem is that it’s now almost impossible to restrict warming below this level. In fact we have only a 20% chance of not exceeding a rise of 3.7C.”

Such a rise – greater than any found in the geological or fossil record for hundreds of thousands of years – would rapidly wipe out corals and other eco-systems, extinguish thousands of wildlife species and create glo-bal food shortages.

Over centuries it would risk melting both the Greenland and West Antarctic icecaps, raising sea levels by a dozen metres.

“I cannot express the level of hope for humanity in precise percentages but I can say that whatever action we take is worth taking. It is a massive challenge and we cannot afford delays,” he said.

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