"There are lots of whorehouses in Macau,” Tom confided to me under his breath in a crowded bar in Islington one Thursday night. “It was my first time in Hong Kong and I remember getting a ferry to one of the brothels where there was a madam and a security guard. On that occasion I didn’t have full sex with the girl, but all my friends did.”

Tom was 23 when he jetted out to Hong Kong to visit friends in 2001, but even then he was no stranger to brothels: it was the fourth time that he had sought the services of a prostitute. He is the sort of young man of whom most mothers would approve, a 29-year-old teacher who is good-looking, well educated and respectful. Yet on his worldwide travels he has paid for sex in several countries, including Australia, the Netherlands and Thailand.

The stereotypical “John” who uses prostitutes is a middle-aged, empty soul whom you might spot slinking around red-light districts in an outsized mac and stained trousers. The uncomfortable truth, though, is that most men who pay for sex are just “regular guys” — colleagues, brothers, fathers, sons and lovers.

Volumes of research have been published on trends among sex workers across the globe — studies on drug use, on the spread of STDs, on the impact of prostitution on society. Yet as a study published in the British Medical Journal in 2005 pointed out, “far less is known about the men who pay for sex”. That study found that the proportion of British men who reported paying for heterosexual sex had increased from 5.6 per cent in 1990 to 9 per cent in 2000. Of these, the largest group were in their mid-twenties to mid-thirties, living in London and either single or divorced.

I realised that, as a single woman in her late twenties living in London, I am surrounded by this demographic. And given that a small but significant proportion of the men identified in the study were apparently upstanding types who slept with prostitutes in secret, I decided to see if I could persuade a few of them to confess.

It took some digging — and a fair amount of tongue-loosening lager — but I found that in some cases the kind of man whom I’d be happy to take to tea with my mother was also the type capable of paying for sex.

Meet Sam, a 30-year-old Cambridge-educated business consultant. He is well spoken, well educated and was brought up a strict Roman Catholic. This did not, however, prevent him from making his way through the red-light district in Amsterdam in search of sex.

“She wasn’t trashy, she was the classic Swedish type,” he insists, describing the woman he chose from one of the windows (I have seen these shop-window women myself and know that some of them look pretty intimidating). “It was such a strange thing for me to do — quite out of character — but I wouldn’t say that physically there was much difference from sex with a girlfriend.”

It is difficult for a woman to understand what it is that a prostitute can offer these perfectly attractive men that a free sexual encounter — be it a one-night-stand or in a relationship — cannot. In an age when women are more sexually liberated and “strings-free” sex is a greater possibility than it ever was before, why are more and more young men choosing sex with a pro?

Disconcertingly, the men to whom I spoke suggested that lack of any emotional obligation is one of the most appealing attributes of paying for sex. “It’s just a case of getting something out of the way,” says Tom, who after his fifth (and, at the time of writing, final) encounter described how he felt “a very cold reaction, very emotionless — you’ve lost that pent-up aggression and you just want to get out of there.”

“I have felt more guilt after one-nightstands than I have felt after going to a prostitute,” says Sam. “As long as prostitution is done in a legal and consensual way, there is almost more honesty in it than in picking up a girl in a bar, where you are toying with people’s emotions and giving false impressions in order to get something physical.”

In the real world — that is, the world where sex stems from boy-meets-girl rather than boy-pays-girl — there are always emotional obligations attached, no matter how casual the liaison. Neither Sam nor Tom is an emotional vandal, the sort of man who swaggers blithely through women’s lives with a philosophy of love ’em and leave ’em.

They see themselves as the good guys, the ones who don’t want to lie, cheat and make promises that they can’t (or won’t) keep to have sex. So, with what seems perverse logic, they sleep with prostitutes instead.

“With a prostitute you both know what you’re doing it for,” says Tom. “She’s doing it for the money, you’re doing it for sex. I’ve had guilty feelings [after visiting a prostitute] but never the same as I’ve had with a one-night stand.”

Only one thing guarantees this understanding: money. When a man visits a prostitute, the mere act of handing over cash for services removes, in his mind, all emotional obligations to her.

“Money displaces the emotions. It frees you from that bond, that responsibility,” explains Sam. “The distance you get from exchanging cash for sex means that afterwards you don’t contemplate the impact on the prostitute.”

It is that distance — emotional, cultural, social — that makes paying for sex appealing to the young punter. Most prostitutes are women far removed from his normal life — she is not in his clique, he will never see her again, maybe she doesn’t come from the same culture as him or even speak the same language. The BMJ study revealed that this is why in the past five years most men who paid for sex were more likely to do so when they were abroad.

In the UK, prostitution itself is not illegal. But many of the acts surrounding it are, including soliciting, pimping and kerb-crawling, which makes it almost impossible for most full-time prostitutes to operate safely. Forced underground, as UK prostitution is, it is perhaps not surprising that 95 per cent of UK prostitutes are thought to be addicted to drugs, and why many men prefer to go abroad to pay for sex.

Even so, there has been an increase in the availability of paid-for sex in Britain as well as abroad. The researchers pointed to “an increasingly large and diverse sex industry” and suggested that more men are using the services it offers because of a wider cultural acceptance of prostitution.

If prostitution was once a dirty and rarely acknowledged secret, it certainly isn’t now. Rap singers have been mainlining the MTV generation (glued to such television shows as Pimp My Ride) with their self-aggrandising yarns of “hos” and “pimps” for long enough for even the outraged to have become somewhat inured.

Sacha Baron Cohen’s character Borat arrived at the Leicester Square premiere of his new film flanked by a harem of actresses dressed as Kazakh “ladies of the night”, and greeted the crowd with “good evening, gentlemen and prostitutes”. Barely an eyebrow was raised.

Some sex workers themselves have even gone “mainstream”. The unidentified London call girl Belle De Jour attracted 15,000 visitors to her blog every day, and landed herself a book deal into the bargain.

As well as providing Belle de Jour with a route to lucrative notoriety, the internet has also revolutionised the whole sex trade.

“The sex industry is more visible and accessible. Anyone with a computer or a WAP phone can find sex workers, read reviews about them or meet them in clubs,” says Dr Helen Ward, of Imperial College London, co-author of the BMJ study.

“Paying for sex has become one of many options in addition to casual sex, short or long-term relationships, or marriage,” continues Dr Ward. “Some men seem to find it attractive to have sex without emotional commitment, while others just like the excitement of paid-for sex. I hope that by showing how common this is we can start to demystify commercial sex.”

If, as the BMJ study suggested, the proportion of men visiting prostitutes almost doubled in the ten years from 1990, it seems fair to assume that by 2010 that figure will have risen again.

The cold truth is that many men today, regardless of how eligible, rich and dashing they may be, don’t go to prostitutes because they can’t get laid. They go because, frankly, it’s an easier way of getting laid.

So, would I mind if my future husband admitted that in his past he had spent weekends in Amsterdam and Prague seeing prostitutes before we met? Probably. But again, is it really any worse than picking up a girl in a bar and lying his way into her pants simply because he was horny? Having been that girl, now I’m not entirely sure.