With his scruffy jeans, piercing blue eyes and long red beard, Aubrey de Grey looks every inch the eccentric scientist. But in the past year, this self-taught biogerontologist, based in Cambridge university's genetics department, has attracted serious attention for his theories about ageing.

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Mr de Grey argues that radical increases in life expectancy will become possible within 30 years. "As medicine becomes more powerful," he says, "we will inevitably be able to address ageing just as effectively as we address many diseases today." He sees no reason why many people alive today should not live to 150 or beyond. The basis for such a confident prediction is a project he leads called "strategies for engineered negligible senescence" (Sens). This has identified seven types of molecular or cellular damage linked to ageing, each of which "is potentially fixable by technology that already exists or is in active development".

Within the scientific community, Mr de Grey is regarded with a mix of fas­cination and scepticism. Is he a pioneer or a crank? Naive or prophetic? One thing is clear: whether one agrees or disagrees with his theories, he is now difficult to ignore. Jay Olshansky, professor of epidemiology at Chicago School of Public Health, admits: "I am a big fan of Aubrey. We need him. I disagree with some of his conclusions, but in science that's OK. That's what advances the field."

But equally significant are the ripples of interest that Mr de Grey is generating outside the scientific community. He has rapidly emerged as the British figurehead of a new political movement, which has steadily been gaining ground on both sides of the Atlantic. This movement is known as transhumanism, and its central belief is that advances in science and technology will liberate us from the constraints of illness and ageing and enable us to live longer, healthier lives.

In its more modest form, trans­humanism advocates the embrace of new technologies, such as smart drugs, cosmetic surgery and gene therapy, which can enhance our physical and mental capabilities and make us "better than well". At the more radical end of the spectrum, you find futurists such as Ray Kurzweil, whose recent book The Singularity is Near, argues that: "Ultimately we will merge with our technology . . . By the mid 2040s, the non-biological portion of our intelligence will be billions of times more capable than the biological portion."

Such predictions have provoked a fierce reaction, both from religious and cultural conservatives, who see trans­humanism as an assault on human nature, and from the liberal left, which sounds alarm bells about the implications for equality and human rights. Francis Fukuyama, the US academic, has described transhumanism as "the world's most dangerous idea".

Yet as the technologies for human enhancement start moving from the pages of science fiction into the laboratory, and eventually into the marketplace, these responses are no longer sufficient. The basic impulse behind transhumanism is a progressive one: a desire to extend current models of medicine and healthcare in ways that would enable us to live longer, fitter and more fulfilling lives.

Provided enhancement technologies are carefully regulated, and opened up to genuine public debate, there is no reason why they should not enjoy widespread public support. Most of us, given the choice, would seize the opportunity to live well beyond our allotted "three score years and 10", even if this required us to take a cocktail of new drugs. The explosive growth in cosmetic surgery shows just how quickly attitudes can change, with enhancements that were once taboo now part of the diet of television makeovers and lifestyle magazines.

The big question is who will bring human enhancement and life extension into the mainstream. Politicians and business leaders, who are already struggling to cope with rising pensions and healthcare costs, may be understandably reluctant to speculate about a world in which we all live (and work?) well into our second century.

Mr de Grey sees himself as a crusader, making enough noise to wake us up from the "pro-ageing trance" that prevents us seizing these opportunities. He has a point. What is politics for if not to improve the quality - and length - of our lives? The transhumanists have done us all a favour by drawing the lines of a political battle that is yet to be fought.

The writer is head of science at the think-tank Demos, which today publishes Better Humans? The Politics of Human Enhancement and Life Extension (www.demos.co.uk)