When my friend, Suzanne, arrived at my door, furious and in tears, after finding husband, Michael, was having an affair, she was no doubt seeking sisterly support for her divorce plans.

However, once she’d calmed down, I suggested she turn a blind eye as this fling would end of its own accord.

Enraged, she demanded: ‘How can you make light of something so serious?’

The consequences of men being sex-starved by their wives are deeply worrying. For such a sexual drought has a profoundly negative effect on our society

My reply? ‘But how can you throw away a good marriage?’

For Suzanne, in her rage, was ignoring a large elephant in the room: the reason her until then decent husband had been driven to an affair was simple. She wasn’t having enough sex with him. After months of frustration, he was forced to seek relief elsewhere.

As a social scientist — I’m professorial research fellow at think tank Civitas and was a senior research fellow at the London School of Economics — you might wonder why I’m so concerned by an all-too common tale.

Men who are starved of sex by their wives are, after all, the butt of many a comedian’s joke.

I’ve found that deep sexual frustration results in men having affairs and then, all too often, divorce and family breakdown

But like many of the men I’ve discovered through my years of research, Michael is experiencing what I call a male sexual deficit.

The consequences of men being sex-starved by their wives are deeply worrying. For such a sexual drought has a profoundly negative effect on our society — fracturing families and potentially leading to violence and crime.

I’ve found that deep sexual frustration results in men having affairs — which was the case with Suzanne and Michael — and then, all too often, divorce and family breakdown.

Sexually starved men are more likely to visit prostitutes, view pornography and, in the worst cases, even molest other women.

So insisting on fidelity within a marriage is all well and good, but unless women ensure they are also having enough sex with their husbands, they are calling catastrophe into their lives.

Sexless or low-sex marriages are far more common than many realise — one sex survey in Britain found a fifth of women, aged from 45 to 59, had been celibate for more than a year.

Sexually starved men are more likely to visit prostitutes, view pornography and, in the worst cases, even molest other women

Well over a third of adults quizzed for a study reported not having sexual intercourse in the previous month. I found the same pattern among people who talked to me for my book, The New Rules.

And it is, make no mistake, mainly women in long-term relationships who lose interest in lovemaking — not their husbands.

Younger men experience sexual desire twice as often as young women, while older men feel aroused four times more than women in the same age group.

This gap in desire between men and women is seen in every country and culture where sex surveys have been done. The received wisdom that men always want more sex than their wives is not a stereotype, but a fact.

However, until the age of 25, there is no difference between the sexes. But, interestingly, by 35, when most of us have settled down, and women, unlike their male partners, are reaching the end of their fertile lives, men — almost to a man — want more sex than their spouses.

A fifth of women, aged 45 to 59, had been celibate for more than a year

Women’s sexual desire tends to decline after 35, though some have a late-flowering sexuality after the menopause.

That being said, in the first two years of a relationship, no matter at what age, novelty does prove an aphrodisiac, even for the female of the species, and couples make love about ten times a month.

Six years in, however, twice a month is the norm — and that’s nowhere near enough for most men. They feel the urge far more frequently, partly due to their higher levels of the hormone testosterone and partly because they can be fertile until old age.

And while in the first three years male and female partners are equally likely to instigate sex, after that point, three-quarters of couples report it is the man who makes the advances.

In fact, a quarter of men in one survey said that, given the chance, they would like sex daily. It should come as no surprise, therefore, to learn that British men are twice as likely as women to admit to having affairs, while one in 25 confesses to having paid for sex during the past five years.

Insisting on fidelity within a marriage is all well and good, but unless women ensure they are also having enough sex with their husbands, they are calling catastrophe into their lives

I’d bet that many of the men who revealed this have wives who are reluctant to have regular sex.

So, where does this leave long-term relationships? With a problem, in my view, that can only get worse.

One reason is that perhaps for the first time ever, there are 6 per cent more men in the world than women. While there have always been a greater number of boys than girls born, historically more men would die in wars, leading to a higher proportion of women in most societies.

But the absence of a world war for more than 70 years means there is a surplus of men competing for fewer women.

Also, these women can earn their own living so no longer have to rely financially on men.

In the past, wives may have felt obliged to offer more sexual entertainment than they were minded to, due to this dependence.

Nowadays, though, they have a lot more autonomy over their sex lives and, if they do not have the desire — as many say they do not — then they’re less willing to lie back and think of England.

Women’s sexual desire tends to decline after 35

Fewer women in the population, plus a rise in independence, combined with the increasing reluctance of women to have regular sex with their husbands can, to my mind at least, only lead to one thing: affairs.

While some of the women these men are having affairs with are free agents, others are married or in long-term relationships and seeking the thrill, and novelty, of sex with someone new.

Though they are uninterested romantically in their own sex-starved husbands, they experience a surge in libido that comes with a new relationship.

More worryingly, there is little doubt, in my view, that sexual frustration can lead to assaults on women, though I am in no way excusing this behaviour.

But do I see lack of marital sex as a justification for men having affairs? Yes, I’m afraid so. For what else are men who need sex regularly to do when married to an unsympathetic wife?

Take the case of my friend, Suzanne, whose husband cheated on her. She had pretty much lost interest in Michael after their son was born. He was a beautiful, happy, loving child and she basked in his unconditional adoration.

Sexless or low-sex marriages are far more common than many realise — one sex survey in Britain found a fifth of women, aged from 45 to 59, had been celibate for more than a year

She had fallen in love, in an entirely new way, with the little boy and, with a full year’s maternity leave to enjoy this new relationship, needed no one else.

Then came the bombshell of the affair. Michael, however, was sublimely unaware that Suzanne knew of his fling.

Not only did I advise her to ignore the infidelity, I told Suzanne she needed to change her attitude towards her husband.

‘Let Michael share the baby with you,’ I said. ‘He will fall in love with him, too, if you allow him in.

‘He needs to feel welcome when he comes home, not an intruder on a private love affair.’

My feeling — though I didn’t think she would appreciate me spelling it out at that point — was that, as they became closer in their daily lives, Suzanne would be more inclined to make time for her husband in the bedroom. This would remove his urge to have his needs met elsewhere.

A quarter of men in one survey said they would like sex daily

Reluctantly, Suzanne agreed to try my strategy and the rest followed naturally.

To her surprise, Michael responded with visible delight, overjoyed at being offered his place as father and husband again.

They’re still together, and years later barely recall those emotionally turbulent times.

I’m a social scientist, not a relationship counsellor, and therefore not in the business of giving advice.

Though the days of women exchanging sex for financial security provided by their husbands are gone, we need to find new ways to trade our wants and needs for theirs.

Men are definitely open to negotiation on this: If he wants more sexual treats, tell him that the deal is you get more help with the washing up, a meal in a lovely restaurant or a new dress.

Men, as we know in our heart of hearts, will have affairs, or perhaps even worse, when faced with sexual starvation and the inevitable resentment that causes.

The cure, put bluntly, is as simple as that for any form of starvation: feed it, feed it, feed it.

The New Rules: Economies Of Desire by Catherine Hakim (Gibson Square, £9.99), available from mailbookshop.co.uk or by calling 0844 571 0640.