Every sex survey conducted this century has revealed the same apparent fact: men have vastly more sexual partners than women. The latest large-scale survey, conducted by Wellcome and first published in 1992, showed that men had, on average, 9.9 different partners over a lifetime, whereas women had only 3.4.

A new French survey has shown that men claimed 11 lifetime partners, as against 3.3 for women, and a Swedish survey found that twice as many men as women had claimed three or more partners over the previous year.

Commenting on his findings in the Fifties, Alfred Kinsey, author of the first such surveys into human sexual behaviour, said: 'Consistently, at every educational level and for every age group, males reported incidence and frequencies which were higher, and in some cases, much higher, than those reported by females.'

In the intervening years we have had the Sixties, the Pill, the permissive society - and apparently nothing has changed. But a medical sociologist, Dr Colin Francome, of the University of Middlesex and a Sixties person himself - he was at the London School of Eonomics from 1964 to 1967 and claims 25 different partners by the age of 25 - believes the figures are wrong, have always been wrong and cannot be believed.

A minute's thought, he says, would tell you that it is an impossibility for men to have three times as many different partners, on average, as women. If this were the case, where are all those extra women coming from? Dr Francome believes that nowadays, at least, the opposite is true - women probably have far more sexual partners than men.

How does he arrive at these conclusions? On the first point, that men have more partners than women, he says: 'Whenever these figures are questioned, authors of the surveys point to 'promiscuous women outside the sample'. But why are such women always outside every single sample?

'And if we take another red herring, prostitutes, we can soon see that the figures are statistically insignificant. Kinsey specifically excluded prostitutes from his findings, and all the surveys where this question is asked show that less than 7 per cent of men have ever paid for sex, and of those, 38 per cent have paid only once.

'Only one in 140 men have had sex with more than 10 prostitutes - a figure which cannot account for the discrepancy.'

Dr Francome, who has written many letters and articles in medical journals pointing out the inherent ridiculousness of the figures, believes the real reason for the discrepancy is a double standard in how the sexes respond to questioning. He said: 'From my own research, I've found that women only ever report long-term or significant relationships, whereas men carefully add up every single sexual encounter, including casual affairs.

'We've found that young boys, particularly, lie like mad about how much sex they've had and with how many partners. But girls are still ashamed to admit they've had more than three different men. It seems that women conveniently forget the casual encounters, or simply do not include those with whom they once had a one-night stand.'

So if it is true that women have indeed had more sexual partners than men, how has this come about? 'For this,' says Dr Francome, 'you have to look at our habits when on holiday abroad. I have carried out a lot of research among ethnic groups, particularly in countries like Greece and India, and I've discovered that the Shirley Valentine syndrome is common, that women frequently have affairs with local men.

'But it's almost impossible for a Western man to have an affair with a Greek woman, for instance. Young Greek girls are kept locked up, and most married women would never dare to have a sexual encounter with a British man.

'In India, it's the same story. It would be very difficult indeed for a British man to persuade an Indian girl to have a sexual fling, and the idea of going to a prostitute in India is not very appealing for the average Western man.

'But British or Western women can have their pick of Indian men. If they want to, they can have a passionate holiday affair and, these days, an increasing number do. Again, what happens is the very opposite from what we imagine.

'It's popularly imagined that men have wild flings with native girls when they go away on holiday or on business trips. In fact, unless they're interested in paying for sex with a prostitute, it's extremely unlikely to happen.'

Another factor is that in every sex survey, it seems that boys have sex at a far earlier age than girls. 'The truth is that girls start earlier than boys - and often finish later. These days, at least, many women are having passionate sexual encounters in their sixties, seventies and eighties, with younger men - when men of the same age have long forgotten all about it, or can no longer perform.'

It also seems possible, says Dr Francome, that men as well as women have more sexual partners than they are ready to admit. 'The Wellcome survey's figure of around 10 different partners during a lifetime seems very low for both sexes,' he said. 'I would imagine the truth is nearer to 15 or 20 on average, for both sexes - with the women having slightly more partners because of the extra men from abroad.'