Having weathered the public storm over BSE, GM foods and cloning, Sir Robert May (right) tells Steve Farrar that he is looking forward to a fresh challenge as the new president of the Royal Society.

Sir Robert May enjoys a game of contract bridge. He has been playing it for four decades and by all accounts, the government's chief scientific adviser is rather good. As his five years in Whitehall draw to a close, May has come to regard the game as vital experience for survival within the machinery of government. It involves working in partnership with someone in a fog of uncertainty, calculating the risks, doing the right thing and then watching the cards fall badly before starting a new game without recrimination. "It was the only major training I had for administration," he says.

Contract bridge suits May's mind. Friends and colleagues regard the 64-year-old Australian as adept at focusing his considerable intellect on a problem and getting quickly to the heart of the matter.

It is an ability that has been central to a meteoric career that has taken him through Sydney, Princeton and Oxford universities, to the heart of British government and, soon, into one of the most prestigious posts in science - president of the Royal Society.

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Henry Horn, a friend from Princeton, says: "Bob's ego, his self-assurance and his competitive spirit exceed those of anyone I have known. But he invariably uses his talents in constructive service to his community. He is the kind of person about whom legends will arise and songs will be written."

Any songs written about his time as chief scientific adviser would surely tell a tale of victory in the face of adversity: the BSE inquiry, genetically modified food and worries about cloning have severely shaken public confidence in science. May responded by adopting the role of a voice of reason, calmly and pertinently explaining the scientific facts without fudging to court political favour. He admits that he was surprised at how important this aspect of his job would become.

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As head of the Office of Science and Technology, working closely with the science minister, with direct access to the prime minister, and with a central role in coordinating science policy across government departments, he saw his role as marshalling the arguments in support of the science base and those trying to exploit research.

He praises the government for recognising that the science base is the bedrock of economic performance and is confident that no one manages the available money better.

But he adds: "We need to do a much better job at wide consultation and thinking through the consequences so there is a general feeling of public confidence that the government is on top of things."

May's academic career began at the University of Sydney in 1953, when he studied chemical engineering. He topped his classes, developed a passion for snooker, chess and tennis and came into contact with the world of research.

"It was clear to me that this was the kind of life that could be immensely enjoyable - playing a game with nature where the challenge is to try to work out what the rules are," May says. So he embarked on a PhD in theoretical physics.

Bob Hewitt, an undergraduate at Sydney when he first met May, and now a professor there, remembers him as an impressive, though sometimes fearsome lecturer.

"Some people were frightened of him," Hewitt says. "If you got on his wrong side, he would cut you down to size."

Authority was no refuge. One luminary, having delivered a lecture, was disconcerted when May prefaced his first question with the observation that, while the seminar was both new and creative, the new bits were not creative and the creative bits not new.

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But many find his bluntness refreshing, and anecdotes of his more choice put-downs have a certain currency among his friends and colleagues.

In 1969, at the age of 33, May became the youngest professor at Sydney. He had an obvious flair for the applied mathematics needed to probe the workings of the world, yet it was in biology, not physics, that he was to make his mark.

May's odyssey into ecology began when he realised that an emerging field of mathematics, chaos theory, could help explain why some populations within complex ecosystems seemed to fluctuate at random. He took on a succession of complicated ecological problems, determined the essentials and subjected the resulting models to rigorous analysis.

A prime example emerged from a collaboration with Roy Anderson, a professor at Imperial College, London. The pair successfully pioneered the ecology of infectious disease and correctly predicted in 1988 that Aids would alter the demography of Africa.

May's determination to succeed helped him, in 1996, to win the Crafoord Prize, biology's equivalent of a Nobel. But his competitive streak is not reserved for the laboratory. When Bob walks his dog, says one friend, even the dog knows it is a contest. This attitude is most visibly expressed in his passion for sport. This he views as a vital outlet for his energies, as well as an opportunity to formulate ideas and make decisions.

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He actively encourages colleagues to take part, which could mean playing football with students at Princeton or "real tennis" with friends in Cambridge, discussing policy while running with Sir John Krebs, head of the new Food Standards Agency, or tackling scientific conundrums while hill walking with collaborator Anderson.

May is also admired by colleagues for his loyalty and his support of bright young pupils, taking time to answer questions and read manuscripts.

"I don't understand why people become engaged as university faculty if they don't enjoy teaching undergraduates," he says.

This experience of academe has heavily influenced his work in public life.

One of the first things he did as head of the OST was to turn his mathematical skills to public administration by drawing statistical analyses from the vast quantities of journal citation data. This enabled him to get a grip on how the UK's scientific output compared with that of other nations, backing his arguments with concrete figures.

His flair for administration had emerged at Princeton, where the volume of external funds doubled in real terms while he was chair of the university's research board. But it was his ability to cut through the waffle, combined with his ability to explain issues in plain English, that made his advice invaluable to ministers.

At first May did ruffle a few feathers. But Ian Taylor, minister for science and technology from 1995 to 1997, defends May's approach. "There's no point in having a chief scientific adviser who keeps out of trouble - you have to have a free thinker."

It is impossible to know how much of an impact May has had. His advice has certainly been heard, yet ultimately, decisions rest with politicians.

By his own admission, the issues he raised directly with Tony Blair, such as the state of the science infrastructure or the cuts in defence research spending, have suffered varied fates. But all things considered, science has done well out of government in recent years.

One direct legacy is the guidelines May drew up on the use of scientific advice in policy-making to rebuild public trust in science through increasing openness.

May was elected a fellow of the Royal Society in 1979, though his application for a Royal Society Professorship almost a decade later was more controversial.

Herbert Huppert, professor of theoretical geophysics at the University of Cambridge and a good friend, recalls: "There were some people on the council of the Royal Society not at all keen on having him, saying he was somewhat past his sell-by date."

Yet he won over the doubters, was subsequently elected to the council itself and, after Sir Aaron Klug's term ends in November, will become president.

He is keen that the society maintains its progress towards becoming the voice of UK science: "I think it has taken huge steps towards becoming a more inclusive and open place under Aaron Klug," he says.

Yet it is likely that his personality, talents and experiences in government will see the new president raise his public profile still further as the Royal Society continues to involve itself in the controversial scientific issues of the day.

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