In the past couple of years the horrors of sex trafficking have been graphically exposed. It is now known that criminal gangs, usually from eastern Europe, offer innocuous-sounding jobs in restaurants and bars to young women who discover too late that their real destination is a brothel or massage parlour in the UK.

Everyone agrees that this modern form of slavery is evil and there are loud demands for a crackdown on traffickers, such as the Albanian gang that was sentenced to a total of 63 years in prison at Southwark Crown Court just before Christmas. Agron Demarku, 22, and his brother Flamur, 34, were the ringleaders in an operation that ran brothels in west London. One 16-year-old girl from Lithuania was forced to have sex with up to ten men a day, and the scale of the enterprise can be deduced from one thing: a single brothel in Hounslow took between £3,000 and £18,000 a day. The Demarku brothers also traded women with other traffickers. On one occasion, reminiscent of a Roman slave market, they were filmed selling a girl for £4,000.

Such stories rightly cause an outcry, but there is something un-settling about the way trafficking is discussed, as though it were all about foreign gangsters and their victims. Why do these men (and occasionally their female accomplices) go to all the trouble of duping women and girls on the other side of Europe and in south-east Asia, and then transporting them to this country? How has sex trafficking become the third most profitable illegal trade in the world, after arms and drugs? Who, to put it bluntly, are these young women being forced to have sex with each day?

The answer certainly isn't foreign men. It is time to confront the fact that, in flats and massage parlours up and down the country, British men are paying money to be "serviced" by foreign women who live in terror of beatings and other punishments. In a laddish culture where women are commodities to be paraded in magazines such as Loaded and Nuts, paying for sex has lost virtually all its stigma; female celebrities collude in the notion that pole dancing is just a bit of fun, while visiting brothels has become the natural end to a blokes' night out or a stag weekend. So acceptable has using prostitutes become that punters post boastful "reviews" of women on websites.

More British men are buying sex; research published last month showed that the number who admitted using prostitutes doubled between 1995 and 2000. They are a minority - 4 per cent admitted having paid for sex in the previous five years, and one in ten over a lifetime - but there is no reason to think the trend has reversed. Research from Sweden tells us something about the kinds of men involved: there, one in eight adult men has paid for sex at least once and the majority are or have been married or cohabiting. In other words, it isn't weird loners who are driving this modern slave trade, but ordinary men - fathers, husbands, sons and brothers. And the effect of their behaviour is showing up not just in the sheer number of people employed in the sex trade in this country - 80,000, according to the police - but in an explosion of sexually transmitted diseases.

In spite of all this, the old blame-the-woman mentality ensures that when trafficked women are rescued they still tend to be treated as illegal immigrants rather than victims of crime. According to Amnesty International, they are more likely to find themselves on a plane than in a refuge where their injuries can be treated; this country has just one such refuge, part-funded by the Home Office, while Italy has 200. Nor has the British government signed a ground-breaking Council of Europe anti-trafficking convention that would give victims rights for the first time (ministers say its provisions, which include a 30-day recuperation period, would be a "pull factor" for illegal immigration).

Voices are frequently raised to suggest that women and girls know what they are doing when they start selling sex, that they choose this way of life and find themselves better off than they were. Such claims ignore virtually all the facts, which have nothing to do with gilt-and-velvet Parisian brothels or the "happy hooker" stereotype of the 1960s. The Poppy Project, which runs the refuge for trafficked women, has found that there are 730 flats, massage parlours and saunas selling sex in London alone; excluding Westminster, each London borough has, on average, 19 sites to buy sex, with between four and eight women per site. Four-fifths of the women are foreign, mainly from eastern Europe and south-east Asia. British police carried out 343 operations against traffickers in the 12 months to last March, arresting 1,456 people and seizing £4.5m in assets. In effect, the sex trade has been industrialised, with trafficked women expected to "service" as many as 40 clients a day. The competition from brothels using captive women has pushed down prices on the streets, which means women are often expected to provide unsafe forms of sex to get by.

Research published in 2001 showed that almost two-thirds of prostitutes in three cities said their main reason for selling sex was to fund a drug habit, and the Home Office estimates that 95 per cent of street prostitutes use heroin or crack cocaine. Most prostitutes in Britain come from poor backgrounds, more than two-thirds enter the sex trade before the age of 18, and half have suffered sex abuse at home before being taken up by pimps. None of this supports the arguments of those who claim that prostitutes and trafficked women are making a free choice or that the answer to both problems is regulation - legalising some or all aspects of the sex trade.

Far from containing it, legalisation would allow thousands more women and girls to be drawn into prostitution without any demonstrable decrease in violence or involvement of criminal gangs. The European countries that have experienced the biggest increases in numbers are those where there are elements of legalisation, namely Germany, the Netherlands, Denmark and Italy; in the Australian state of Victoria, often cited by campaigners for legalisation, the number of prostitutes is said to have doubled between 1994 and 2002. (Australia and the Netherlands also have the world's highest number of sex tourists per capita, supporting the proposition that legalisation normalises the act of buying sex.) There is evidence, too, that legalisation acts as a "pull factor" for traffickers; in 2003 Amsterdam city council decided to close down its street tolerance zone, the mayor declaring that "it appeared impossible to create a safe and controllable zone for women that was not open to abuse by organised crime".

What is becoming clear is that men who use brothels, massage parlours and street prostitutes are the missing link, invisible in most discussions of the sex trade. This has led to a bizarre anomaly: men who supply girls and women for sex are liable to receive lengthy prison sentences, but those who use them, and create the demand in the first place, go scot-free. When a brothel or massage parlour is raided by the police, the customers are allowed to leave before it has even been established whether the women are working there voluntarily. This absurdity was illustrated when, in September, 19 women were rescued in a raid on Cuddles, a massage parlour in Birmingham. West Midlands Police announced a big victory in the campaign against trafficking. The following week it emerged that six of the 19 were being held at the Yarl's Wood detention centre in Bedfordshire, awaiting deportation, yet all the men present at the time of the raid were released without charge.

This is happening up and down the country, even though it is clear in law that men who have sex with trafficked women are committing rape: women who have been threatened and beaten into working as prostitutes cannot give meaningful consent, as Harriet Harman argued in a landmark speech last year. A Home Office minister, Paul Goggins, agreed with this proposition in a discussion with me on BBC Woman's Hour last autumn, and a second minister, Tony McNulty, confirmed it in the House of Commons. With such clear ministerial support, the first rape prosecution of a prostitute's "client" is long overdue.

The willingness of so many clients to pay for sex without bothering to find out whether or not the woman has been coerced is significant for another reason, however, because it exposes the pernicious assumptions at the heart of prostitution. One is the rarely challenged claim that there is something peculiar to male sexuality which makes men entitled to sexual release whenever they want it; another is that women are a class from which men should expect to get sex, regardless of the damage they inflict on individuals. In that sense, it is just as much an abuse of human rights as conventional slavery, which assumed that Africans could be bought and sold for use by white people. Naturally this argument arouses furious resistance - after all, it threatens the entire sex trade - and is often caricatured as an anti-sex position when it is actually the opposite.

"Prostitution is sexual exploitation, one of the worst forms of women's inequality, and a violation of any person's human rights." So wrote a group of survivors of prostitution and trafficking from five countries who launched a manifesto at the European Parliament last autumn. Since 1999 this has been the official view of the Swedish government, which in that year removed penalties for selling sex and imposed them instead on men who buy it. Gunilla Ekberg, a special adviser at Sweden's ministry of industry, employment and communications, explained the thinking behind the law: "In Sweden it is understood that any society that claims to defend principles of legal, political, economic and social equality for women and girls must reject the idea that women and children, mostly girls, are commodities that can be bought, sold and sexually exploited by men." In the most radical approach ever adopted by any state, the Swedish government argues that "the legalisation of prostitution will inevitably normalise an extreme form of sexual discrimination and violence and strengthen male domination of all female human beings". Men who seek to buy sex can be punished by a fine or up to six months in jail, while women (and men) who sell it have a right to assistance to escape from prostitution.

The effect has been dramatic. Official figures show that the number of women involved in prostitution fell from 2,500 before the law came into force in 1999 to 1,500 in 2002. By 2004 the recruitment of women into street prostitution had almost halted. With a population of nine million, Sweden is estimated to have only 500 street prostitutes, while neighbouring Denmark, with a population just over half that size, had between 5,500 and 7,800 in 2004, half of whom, it is estima-ted, were victims of trafficking.

Supporters of the law say it has also had an impact on trafficking into Sweden, with the National Criminal Investigation Department (NCID) reporting that the country is no longer an attractive market for foreign gangs. Intercepted telephone conversations show that pimps and traffickers express frustration about setting up shop in Sweden, preferring to operate in Denmark, Germany, the Netherlands and Spain. In its 2004 report the NCID concluded that the law "continues to function as a barrier against the establishment of traffickers in Sweden"; it estimates that roughly 400-600 women are trafficked into Sweden each year, compared with between 10,000 and 15,000 into Finland. The law's opponents claim it has made street prostitution more risky because the few remaining clients tend to be more "perverted", but most of them concede that it has reduced demand.

The Swedish example could hardly be more relevant to the UK, as the Home Office announced its new "co-ordinated strategy for prostitution" in England and Wales. The proposed policy includes some steps in the right direction. It reverses plans, for example, to give local authorities discretion to set up "tolerance zones", and proposes ways of helping women escape from the sex trade and of clamping down on kerb crawlers. It also includes an utterly misguided proposal: to permit small brothels where two or three women can work together - an idea wide open to abuse by traffickers. This is an aberration. A philosophical shift seems to have begun, and as long as it is combined with realistic and properly funded measures to help women, including access to education and decent housing, we should welcome it. Trafficking and prostitution are expressions of a gross form of misogyny which, by denying bodily integrity to the weakest women in society - young, poor, sexually abused, dependent on alcohol or drugs, foreign and coerced - denies it to women everywhere.

A life of prostitution
95% of female street prostitutes in the UK use heroin or crack cocaine
76% of the public favour introducing some form of regulation to the sex industry
69% of prostitutes say they report no or hardly any attacks to the police
60% of prostitutes say they have been beaten up or raped in the past year
55% of prostitutes say men have refused to pay them for their services
50% of working prostitutes are under the age of 25
27% of the public believe prostitution should be stamped out altogether
10% of men admit to having used prostitutes
1% of prostitutes say they have stopped street sex work as a result of police activity

Research by Sam Alexandroni