If we were designing men and women to deliver maximum sexual satisfaction to one another, we would not start from here. The reason, as Shere Hite noted, has to do with the position of a tiny, but neglected organ – the clitoris.

Conventional sexual intercourse, in which the penis is inserted into the vagina, may be an efficient method of reproduction but is doomed to failure when it comes to maximising sexual pleasure – at least for the woman.

The author of the Hite report, one of the most detailed surveys of sexual behaviour ever carried out, says doctors, therapists and the public share a collective blindness about this simple anatomical fact which determines the way in which most women achieve orgasm.

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The key, according to Ms Hite, is that women have orgasms more easily when masturbating than when having intercourse. This is because the clitoris, the stimulation of which leads to orgasm, is situated above the entrance to the vagina, where it is mostly inaccessible to the thrusting movement of the penis.

"The overwhelming majority of women, according to my research, can have orgasms easily during masturbation. So why not also during coitus? The answer is that during masturbation women choose to stimulate the clitoral area. Only rarely, in 2 per cent of cases, does it involve vaginal penetration," she said.

This difference between men and women is fundamental but not widely recognised. For men the stimulation they give themselves when masturbating is similar to that which they receive when having intercourse. For women it is completely different. So it is not at all surprising that the rate of orgasm for women during intercourse is low.

That old cliché about men being from Mars and women from Venus applies not only to their psychology but to their anatomy, too.

Despite the importance of clitoral stimulation to women, the definition of sex is focused on intercourse. This is fine for men, but not at all fine for women, and may account for the high proportion of women that research suggests suffer from "sexual dysfunction".

Ms Hite says it is this limited definition of sex, not women's bodies, that is at fault. Sex should be composed not only of intercourse but also of clitoral stimulation, by hand or mouth. But the sad reality is that although women know how to have orgasms, they rarely feel free to express this during sex with men. Their inhibition not only denies them pleasure but has also put researchers trying to treat female sexual dysfunction on the wrong track.

The fundamental error was committed by Freud who said that the source of sexual excitement transferred from the clitoris to the vagina at puberty. This view was later entrenched by psychiatrists who defined a lack of orgasm during intercourse in women as a disorder. Now drug companies are trying to solve the problem by looking for a female equivalent of Viagra. But by focussing on women's readiness to participate in intercourse rather than helping them to experience pleasure, they risk making matters worse.

Ms Hite said: "The pharmaceutical industry has misunderstood the basics of female sexuality. Putting money into supposed treatments that don't work could mean financing unhappiness and divorce, leaving women's feelings invisible or unexplained, and placing men on insecure ground.

"It risks fostering an atmosphere of fear and confusion in which love, including intense sexual intimacy and experimentation, needlessly becomes an area of conflict rather than pleasure."

"It is not arousal pills we need, but a whole new set of physical relations with each other," she says.

Critics have challenged her analysis on the grounds that it neglects another part of the female anatomy – the G-spot. The G-spot is said to lie a third to halfway inside the vagina, on the upper (front) wall and is claimed to enable some women to experience a vaginal orgasm, in addition to the conventional clitoral one.

Unlike the clitoris, however, the existence of the G-spot has been contested ever since it was first suggested by German gynaecologist Ernst Grafenberg in 1944 (after whose surname it became known in the 1980s). Earlier this year, Italian researcher Professor Emmanuele Jannini claimed to have located it using ultrasound. That was the good news. The bad news was that, according to Professor Jannini, not all women had one.

His study, involving 20 women, suggested those who claimed to experience vaginal orgasms had an area of thicker tissue on the front wall of their vagina, which he identified as the G-spot, while those who had not climaxed in this way had not.

Others disputed the findings, reported in the Journal of Sexual Medicine, suggesting the thicker tissue was actually part of the clitoris which, in some women, extends far beyond its visible tip. MRI scans have shown that the clitoris is in the form of an inverted V, extending from the tip, back and along the vagina, raising the possibility that, in some women at least, it may be stimulated internally as well as externally.

Sexual failure, as all couples know, is not confined to women. If for females it is the location of the clitoris that causes problems, in males it is the performance of the penis. Almost all men experience impotence on some occasions or at some time in their lives.

Masters and Johnson, the American gynaecologist and psychologist who revolutionised sex research 40 years ago with their detailed laboratory studies of the physiology of sexual arousal, described how the human sexual response fell into four distinct phases, for both men and women – excitement, plateau, orgasm and resolution.

The excitement stage is marked by increased blood flow to the genitals causing them to swell. In men, the tissues of the penis become engorged with blood, so that it stands erect, while in women the tissues surrounding the vagina swell and fluid seeps through the vaginal walls, increasing lubrication. The glans of the clitoris enlarges and hardens in a process similar to male erection.

While successful penetration and intercourse depends on the arousal of both sexes, it is the male erection – or its absence – that is the most frequent cause of problems. A common difficulty is that men can get an erection but cannot hold it long enough to have sex. In 75 per cent of men with impotence who have normal neurological and hormonal function, blood flows into the penis normally but flows out too rapidly.

Treatments for impotence have been painful, cumbersome and of limited effectiveness in the past – until the arrival of Viagra in 1997. An effective therapy in an oral tablet, it transformed the approach to male impotence. The Government was so worried by the potential demand that it immediately restricted its availability on the NHS to men with diabetes, multiple sclerosis and other chronic conditions. Even so, it rapidly became a global best seller.

Viagra works by increasing the blood flow to the penis, boosting performance when sexual arousal occurs. Male journalists lucky enough to be asked to test the drug in its early days wrote almost universally enthusiastic reports, proving that it is a rare erection that cannot be improved, even in relatively young men.

A recent study suggested that Viagra has transformed the sex lives of the over-70s who have found themselves able to continue having intimate relations for years, or even decades, longer than in the past. But while men are performing better they are enjoying themselves less. It is women who are reaping the benefits, reporting increased satisfaction with their sex lives, while in men satisfaction has declined. The study was conducted in Sweden and published in the British Medical Journal in July.

Viagra's success prompted drug companies to search for its female equivalent. Could a similar drug do the same for women? Millions have been invested, but women are proving more complicated than men.

Female sexual dysfunction is a more diverse condition than male impotence. Researchers have pointed out that it has four distinct categories: lack of desire, lack of arousal, pain on intercourse and lack of orgasm and that only one of these – lack of arousal – corresponds to impotence in men. Trials have shown that Viagra can help some women with lack of arousal by increasing blood flow to the genitals. But it cannot help the other three components of female sexual dysfunction.

A female testosterone patch, called Intrinsa, launched in the UK in 2007, is claimed to restore the sex drive of women with low libido. It has been shown to boost sexual desire in post-menopausal women, but it is currently only licensed for those with premature menopause caused by surgical removal of the ovaries, of whom there are one million in the UK.

Although testosterone is a male hormone, it is also produced in women at a lower level and plays a crucial role in sexual desire. Levels of testosterone fall after the menopause as do levels of oestrogen.

There has been a fierce debate in recent years about the extent of female sexual dysfunction with one widely quoted study suggesting as many as 43 per cent of women may be affected. Drug companies have been accused of stoking the issue to create new markets.

But some experts say the problem is under-recognised and under-treated. They describe clinics packed with post-menopausal women worried about loss of libido. "My patients complain bitterly of the loss of sex drive and satisfaction, and of difficulty in achieving orgasm. The drug companies have not invented it, we need to have a treatment that is safe, reliable and cheap," said one gynaecologist.

Critics say there is a danger of seeing problems where they don't exist. Lack of desire may be widespread, but it is not perceived as a problem by many women – and men – who may feel relief as advancing years bring freedom from the need, or the demand, to have sex.

This was borne out by a survey of 1,000 women and 450 men in north London, published in the British Medical Journal in 2003, which revealed that 40 per cent of the women and 22 per cent of men reported at least one sexual problem. But those who mentioned "lack of sexual desire" were much less likely to have visited their doctor for treatment than those with other problems. The implication, the researchers from the Royal free Hospital said, was that lack of desire was not necessarily an "obstacle to satisfactory sexual relations".

"For many people reduced sexual interest may be a normal adaptation to stress or an unsatisfactory relationship," they added.

As they age, men and women may hope to achieve some kind of sexual accommodation with one another. Along the way there is certain to be tension, reflecting in part their differing physiology and needs. Men are still expected to make sex happen, and women to respond. That causes some to question the whole notion of female sexual dysfunction. The clinical psychologist, Dorothy Rowe, expresses the cynical view. It is, she says, "something men dream up when women won't do what they want".