Off to a Greenpeace rally via the bottle bank in your eco-car, converted to run on organic carrot juice? Don’t bother. Instead, go for a burn-up in a Ferrari, crank up the heating and wait for the end of the world.

This seems to be the message of James Lovelock, celebrated scientist and creator of the Gaia theory that taught us to think of the planet as a living organism. He declares it is too late to save civilisation as we know it, so save yourself. Find a mountain, perhaps on the island of Cornwall, before the floods arrive — London, he tells me, could be under the North Sea within 50 years.

Gulp. Is this some swivel-eyed old boy with a sandwich board assuring us the end of the world is nigh? Nope. Lovelock is one of Britain’s most revered thinkers. Sure, his Gaia theory — named during a Wiltshire walk by Lovelock’s friend William Golding after the Greek goddess of the earth — was considered cranky back in 1979. But it is now the paradigm in which science is done.

It holds that the planet, far from being just a ball of lumpen matter like Mars, is living and self-regulating: a series of connected systems control conditions; crucially including climate. But so badly has man treated his mistress, Gaia, that she can no longer heal herself.

Lovelock says global warming is caused by industry belching out too much carbon dioxide, farming that eats away at forests, and too many damn people who, because of increased wealth, are pumping out more emissions through everything from their cars to their fridges. The great thaw is now so advanced that the sun’s rays are no longer being cooled by the whiteness of the icecaps, as they are melting away.

Lovelock is no eco-nut with personal hygiene issues: he supports nuclear power and once worked for MI5 as “Q” — inventing whizzo gadgets to spy on Ruskies.

So his warning about rising sea levels caused by global warming puts into alarming relief sedate conferences on climate change and George Bush’s aspiration to cut back a teensy-weensy bit on Middle East oil. Lovelock’s intervention has been described as a “wake-up call”, but could be termed a “thank you and good-night call”.

“It is much too late for insulating your house and all that,” says Lovelock. “Fifty years ago it would have helped. What we need now is sustainable retreat.” As he concedes, it is a “gloomy” prognosis from an otherwise cheery man, born working-class in Brixton but now pottering about a converted Devon mill.

Yet in 20 years he predicts fuel will grow so short it will be rationed. “It will be like world war two,” he says, eyes twinkling. He remembers. He looks puckishly in the pink, chomping on fruit cake baked by his much younger American wife Sandy, but Lovelock knows he is also running out of time: he is 86.

As for London: “There was a three-year period the Thames barrier wasn’t used at all, but in a recent year it went up 24 times. Why isn’t government planning to rehouse people? London is sinking anyway, so global warming is lethal.”

Flooding, caused by the melting of the ice caps, will wipe out entire countries, he contends. Only the more northerly countries will survive. Luckily, this includes chunks of Britain. Then, he suggests, we will have to form nothing less than a new civilisation based not on the creation of wealth but the preservation of the earth. He ends his latest book, The Revenge of Gaia (published by Allen Lane), proposing a manual for human survivors of the coming apocalypse, telling them how to start again, with fewer people leading simpler lives. Meanwhile, as it would be “hubris” to imagine we can save the planet, he reckons it is “natural to think ‘let’s make hay while it lasts’”.

Unlike science-bores, Lovelock talks in the vivid lingo of the science fictionalist: “The Arctic basin,” he declares, “will be home to the desirable real estate.” You suspect he enjoys these little bons mots. By then the Arctic will not quite be St Lucia, but it will be pleasant in an austere sort of way; much of the Third World, by contrast, will be too hot to support human life. So grave is the crisis that he seeks radical solutions.

But his former friends, the greens, are horrified by his call to renew our ageing nuclear reactors — although he insists a few big turnips in the green lobby “privately agree but have told me they couldn’t possibly say it publicly”. His reasoning? There is simply no time to mess around developing alternative energy.