The Joy of Sex introduced a generation to cordon bleu love-making. Twenty-five years later, Liz Hunt finds that its author would rather talk about free verse than free love
"When I first wrote the book people worried if they were doing all these things. Now they worry if they aren't. People will always worry. That is why I wrote it in the first place." And that, dear reader, is all that Dr Alex Comfort, inventor of the modern sex manual and alleged sexual swinger, has to say on the subject of sex.

Perhaps Dr Comfort, now 76, feels he has said it all before, in the hundreds of interviews he has given in the 25 years since his multi-million bestseller, The Joy of Sex, was first published and rapidly sold out. It found an audience who were hungry for the knowledge that would allow them to enjoy to the full the new freedoms from sexual hang-ups that had emerged, along with the Pill, in the Sixties. Dr Comfort provided it, with easy-to-follow illustrations (unbelievably, the bearded Neanderthal man who romped across the pages of that first edition was considered to be a turn-on at the time) and uninhibited prose. He has described the publication of the book as akin to "ripping down the Iron Curtain".

I did try to get him to talk about sex. How had he, a 52-year-old British doctor with a special interest in ageing, accumulated the knowledge for his cordon bleu guide to love-making; was it true that his emphasis on the big toe (page 69 of the new, anniversary edition) as a "sexual organ of considerable versatility, yielding great pleasure" was influenced by his loss of three fingers on his left hand as a boy; and did he really partake of group sex at a Californian nudist colony where he was conducting research?

To no avail. Dr Comfort, whose frail, shrunken appearance belies his bright-eyed, intellectual sharpness, parried each increasingly desperate question with a polite yet dismissive sentence, devoid of any soundbite potential. He absolutely did not want to talk about sex, and certainly not the more explicit items in The Joy of ... . One of his carers suggested that "he didn't really like talking about it" to young [ish] women. So my curiosity about some of the Main Course acts of love - the anniversary edition retains the original's menu approach to intercourse, with chapters on Ingredients, Appetisers, and Sauces - such as "bird song at morning", "little death" and the infamous "goldfish", remained unsatisfied.

He did mention fish, actually, but they were the guppies he had studied in his ground-breaking experiments on ageing at University College in London in the Fifties. His work, subsequently published in Scientific American, disproved the commonly held hypothesis of the time that animals age because they cannot grow beyond a biologically, pre-determined adult size. Guppies grow continuously and in theory, indefinitely; Dr Comfort showed that they aged and died in the same way that mammals did.

He also talked movingly of his love for Ireland, where he had studied briefly as a medical student, and his favourite haunts in County Sligo, the home of Yeats, whose works he quoted at me in a singsong seductive tone.

But we digress - as Dr Comfort intended that we should. He long ago wrote his own script for interviews on The Joy of ... and decided what questions he would or wouldn't answer. Journalists who depart from the script are treated courteously but abandoned until they realise their error and refrain from the ad libbing.

Dr Comfort's reluctance to talk freely about The Joy of ... is due in part to the effort it requires. The smartly-dressed figure dwarfed by the huge chair in which he spends day after day in his north London flat is severely disabled by a stroke which paralysed his right side five years ago. His speech is not affected, but his economy with words is an unwelcome adaptation forced on a man who is not used to rationing the spoken or written word.

Dr Comfort, a physician and scientist of international renown, also enjoyed a reputation as a novelist, poet, playwright and philosopher of some distinction, and was author of around 28 works of fiction and non-fiction before he wrote The Joy of Sex. He had experienced notoriety as an outspoken pacifist, and had served time in jail alongside Bertrand Russell for refusing to be bound over prior to a Ban the Bomb demonstration in Trafalgar Square in 1961. He formed a Science for Peace organisation in the Fifties, and was a founder member of CND. He has even written lyrics to songs composed by the rock musician Pete Seeger. Had he been born a little later, Alex Comfort would have been up there along with the celebrity scientists of the television age such as Desmond Morris, David Attenborough and Jonathan Miller.

He had, throughout his career, been an advocate of greater sexual freedom as the key to mankind's well-being, and in 1962 caused a minor scandal by suggesting that 15-year-old boys should carry condoms. He wrote The Joy of Sex because a friend at the London Hospital Medical School in Whitechapel, his alma mater, told him that sex wasn't being taught properly. It was intended as a serious textbook on human ethology, but evolved in the two to three-week period in which he wrote it into something more, with a working title of Cordon Bleu Sex - a title dropped because of objections from "the cooking people". James Mitchell, of the publisher Mitchell Beazley, a good friend of Dr Comfort, agreed to publish the book and coined its new, inspired title.

"I had all these notes accumulated from years of teaching and research as a doctor, a human biologist and student of sexual behaviour, and my wife was always on at me to write something. But the reaction of the public was amazing. It greatly surprised me," Dr Comfort says. People sidled into bookshops to buy it, explaining how they had been given a "prescription" by their doctor for the book and could they possibly have it in a bag to take home, please. "You have no idea of the attitudes. I remember a woman who did not want to be seen at the antenatal clinic because she didn't want her neighbours to know she was having sex with her husband," he recalls.

Alex Comfort is not particularly excited by the new edition of his magnum opus, which has sold more than eight million copies worldwide. He has described it as an "albatross" that detracts from his other contributions to science and the arts. He is still writing, using his one mobile thumb to tap out his thoughts on a battered manual typewriter, but it is for his poetry - his last collection was published in 1979 and dedicated to his second wife, Jane - that he hopes he will be remembered most. "Poetry," he says, "is the thing that survives a man longest of all his efforts."

To celebrate the 25th anniversary of 'The Joy of Sex', a limited, specially- packaged edition is published by Mitchell Beazley on 25 November at pounds 16.99, together with a paperback version at pounds 12.99 and a pocket book format at pounds 8.