Sexual self-help came into its own in the Sixties, kicking off with Helen Gurley Brown's Sex and the Single Girl and the founding of her Cosmopolitan empire. Ten years later, The Joy of Sex recommended bored couples to look, not between their legs, but to their feet for sexual inspiration - the big toe, the book declared, was 'a magnificent erotic instrument'.
In the Eighties, women's magazines suddenly discovered that sex was a powerful weapon in the ratings battle and titles pushed the boundaries of taste to their limits in their quest to carry the most risque articles about sex.
The recent upsurge in DIY sex therapy came in 1991, when the British Board of Film Classification granted an '18' certificate to Dr Andrew Stanway's video The Lovers' Guide which, along with its companion volumes, has since sold around 750,000 copies in the UK and a further 500,000 abroad. This opened the floodgates for more explicit sexual information so that now practically anything can be shown - even ejaculation - just so long as it is 'educational'.
But just who are these people who are telling us where to put what? What qualifications do they have? Do they practise what they preach? And is it perhaps just a case of those who can, do, while those who cannot, teach?
TONY & WENDY DUFFIELD
Describing themselves as 'lifestyle consultants specialising in sex, romance, relationship problems, and incorporating astrology', the couple gained notoriety when they came together (literally) to work on The Lovers' Guide. They are now best known for appearing on Desmond Morris's The Human Animal. Not only did they make love in front of a film crew but tiny cameras were placed inside intimate orifices to show the physiological processes at work.
Inspired by the success of the programmes Tony, 38, and Wendy, 31, have launched themselves as fully-fledged sexperts. They now have a weekly sex-advice column in Me magazine, a string of 0891 sex-lines, a video (The Love Plan) and a book (Sextrology).
Qualifications for the job? Wendy has 10 O-levels, five A-levels and a business degree; and, of course, they both like bonking. 'We're not porn stars,' Tony emphasises, 'we are researchers.'
Suzie Hayman, 45, knows everything about vibrators: she tested every model for her book, Good Vibrations. 'I find those multi-heads an absolute con, they are no better than the cheap ones,' she says.
Has specialised in sex education since 1976, after training as a teacher. A Relate counsellor and an agony aunt, she sits on the board of the Brook Advisory Centres and the national executive of the Family Planning Association.
Losing her virginity at 17 ('Fireworks didn't go off, but I felt nice all over'), she has had six sexual partners and in July this year married writer Vic Cowan, her partner for the past 20 years. She uses a 'psychodynamic client-centred' approach, to combat what she sees as the biggest passion-killer - lack of self-esteem.
Has confessed that she makes dates for sex with Vic. 'One of us might say: 'Meet at such and such a time in the bedroom'.'
A 48-year-old who looks like a boy scout leader. Born in Bedford, Hodson grew up in the Midlands, swung between obesity and anorexia in his teens, won a scholarship to Oxford, where he studied history and political philosophy.
His first professional foray into the world of sex was as co-editor of the sex magazine Forum, with his long-time partner Anne Hooper. 'People used to tut-tut, but it was an important magazine,' he said.
Became a marriage guidance counsellor at 27, qualified as a psychotherapist when he was 38. First attracted national attention in 1976 through a sex-advice phone-in show on LBC radio. His enticingly titled book 365 Ways To Have A Happy Sex Life (co-written with Hooper) is a collection of problem-page-style letters answered in a syrupy, occasionally prurient, style. Mocked for his capacity to love himself, he says women like him because of his sense of humour and his big bottom.
Her book, Sexual Body Talk, has been published in 13 countries round the world and is dedicated to her husband, educational publisher Ian Grove-Stephensen, 'without whom I never would have discovered sexual body talk'. Yes, Quilliam, 44, believes non-verbal communication is central to understanding, even transforming, relationships.
Lists her areas of expertise as 'finding a partner', 'sexuality and sensuality' and 'relationship crises and trouble-shooting'. Also has a degree in psychology, 10 years' experience as a counsellor, and has written 10 books, including Supervirility and Women On Sex.
'I suppose you could say that the ideal sex expert is like me,' she says. 'Someone who has basic qualifications and has worked their way up through the university of life.' Maintains the problem with academic sexologists is that, despite a string of letters after their names, they may not be any good on the practical side.
Confesses to being turned on by her books. 'I get an idea and think, 'Oh, that's nice.' ' She thinks her sexpert status has 'made me dissatisfied with mediocre sex'. Official 'body language consultant' to the Sun, and working with Relate on a book - subject unknown - to be published next year.
Renowned for her pre-orgasmic workshop for British women, husky-voiced Hooper considers masturbation the key to resolving female sexual dysfunction. As she explains in The Body Electric: 'It's a healer, an energy giver, an alleviator of tension, a gift of self-pleasure.' Now in her fifties, she has been a sexual and marital therapist for 18 years, with problem pages in Best magazine and on ITV's Teletext. Her Ultimate Sex Guide has sold 200,000 copies.
Tips include sexual banquets ('a little honey, syrup or champagne feel good going on over the breasts and navel'), sexological exams ('exploring each other's 'private parts' will bring a new awareness of your genital sensuality') and S & M play ('beat his naked buttocks with your riding crop'). However, in her new book, Anne Hooper's Kama Sutra, she states: 'I'm not very interested in sex practised as a style of gymnastics . . . I've never felt that athletic poses had much to do with my own sex life.'
DR ANDREW STANWAY
'Get to know your genitals,' he purrs. 'A chair presents many interesting possibilities,' he muses. 'You can't have sex all the time,' he states.
A marital and sexual therapist, Stanway first had the idea for an adult sex education film 15 years ago. The censor put a dampener on his efforts until he hit the big time with The Lovers' Guide videos; worldwide, an estimated 5 million people have watched this middle- aged man guide them through the ins and outs of sex.
Well-versed in therapy-speak, he and his wife, Dr Penny Stanway, run a course for women called Listening and Loving, employing the concept of 'empathic listening' - talking like a wide-eyed West Coaster.
He has courted controversy by suggesting that every time a couple has sex there are three people in the bed - the man, the woman and her mother.
DR RUTH WESTHEIMER
A four-foot-seven, 66-year-old Jewish grandmother is the world's most famous sexpert. She was born in Germany and educated in the US, where she took a masters in sociology, a doctorate in education and studied human sexualityat the New York Hospital-Cornell University Medical Center.
First step on the road to global sexual mastery came in 1980 when she briefed the managers of New York's community radio shows on how to pep up their sex education coverage and left with her own 15-minute slot. Her mission is to make sex 'fun, safe, adventurous and fulfilling.'
Likened to Mel Brooks in drag, Westheimer considers her unusual looks an advantage: 'If I'd been a tall blonde in a miniskirt, it wouldn't have worked.' (People with problems might have been intimidated.) Critics say she is motivated by the trappings of fame; she certainly loves her luxuries. 'I could not have afforded Ferragamo shoes if it weren't for the money I make. Bubble bath, champagne breakfasts, that's my life]'
She has written 11 books, has a column in 100 newspapers worldwide, and globally syndicated TV shows. New spin-offs include Dr Ruth's Good Sex Night-To-Night Calendar and a board game, Dr Ruth's Game of Good Sex. Coming soon: an interactive CD-rom version of Dr Ruth's Encyclopedia of Sex.