A correction pertaining to the opinion piece below by Rahila Gupta was printed in the Guardian's Corrections and clarifications column, Monday 1 February 2010

An article on trafficking into the sex trade has been written by the investigative reporter Nick Davies, whose reputation will lend authority to it – although it is a hugely selective piece of reporting of the available research.

The article purports to show that so few women are trafficked into the sex trade that the policy, services and funding focus on it is completely misplaced. The debate on trafficking is bedevilled by the lack of credible data – but the parallels are not with the weapons of mass destruction case, as Davies suggests, which was ultimately verifiable, but with other subterranean issues such as domestic violence or rape. The widely accepted statistic that one in four women experience violence, for example, is based largely on anecdotal evidence and extrapolations from local surveys. It could be similarly taken apart by anyone who wanted to assert that the case was overblown, because ultimately the numbers are unknowable.

The piece opens with a clever piece of sophistry that suggests trafficking does not exist. Davies claims that "The UK's biggest ever investigation of sex trafficking failed to find a single person who had forced anybody into prostitution" – which seems to suggest that prostitution is generally a voluntary activity, an argument developed in the rest of the piece. However, it is actually saying that it failed to find traffickers. I have interviewed police officers who say it is extremely difficult to use the trafficking laws to bring people to justice.

Peter Spindler, the police officer who headed Operation Paladin, a three-month investigation into unaccompanied children entering the country through Heathrow, has talked about the difficulties of obtaining convictions for trafficking. "We've got all the offences, but they are so complicated to prove. We have had a number of convictions for facilitation where organised criminals have been paid to bring children in. The problem with trafficking is that you've got to prove exploitation," he says. In spite of these problems, we discover from a parliamentary answer from Alan Campbell in June that 267 people have been prosecuted under the Sexual Offences Act 2003, which led to 109 convictions, a remarkably high percentage. This fact does not appear in Nick Davies's article, despite his extensive research.

There are other notable absences: there is no mention of the report into trafficking by a home affairs committee, published in May, which gave an estimate of 5000 trafficked women and children in the UK, based on an aggregation of the figures provided by those working in this field. Nor does the article make a distinction between smuggling and trafficking. When Davies refers to the conviction of criminals for "transporting willing sex workers" he is talking of smuggling, where the smugglers and those smuggled in are equally guilty before the law.

On this basis, prostitutes were regularly criminalised and deported before trafficking legislation was brought in to safeguard women who had been coerced into the work. The European convention on action against trafficking in human beings, in its limited way, shifts the focus from criminalisation to the protection of women. It is self-serving and reckless for the sex workers' lobby to argue against trafficking legislation simply because recognition of the scale of the problem undermines a central plank of their argument: that prostitution is freely chosen.

Davies quotes only those sex-worker groups who feel that their right to work as prostitutes is under attack from anti-trafficking initiatives. A recently formed group of ex-sex workers, Esso, believe that only 2% of women freely choose prostitution. Their leaflet declares that they are fighting, "for a world where females are not bought and sold like commodities; our orifices just another currency, our labour and lives and sexuality expendable". Fiona Broadfoot, an ex-prostitute, who set up the Exit project to help women in a similar situation, said they "couldn't put one foot in front of another without taking £400 worth of crack". Even outside the debate on trafficking, there has to be a much more nuanced approach to choice and compulsion. Many women are deliberately addicted by pimps so that they stay on the game in order to finance their habit, while others report that they cannot get through a working day unless they are drugged to their eyeballs.

The UK government's actions are part of a concerted European attempt to tackle trafficking. If sex trafficking is a chimera, then not only the UK but the EU has been duped. To challenge the scale of the problem in the UK, you have to challenge the Europe-wide response. Women are often pushed around various parts of Europe. "Natasha", a 17-year-old Russian girl I met, was taken to Brussels and made to work there before she was sold on to a trafficker in London. Her pimp was convicted and imprisoned for seven years, but only because she finally agreed to the harrowing experience of giving evidence against a man who had terrorised her. Women like her already face a "culture of disbelief" among immigration officials keen to reduce the number of women who get leave to remain in this country on the basis of their experiences. Articles such as this will only make things worse for them.

To get governments to part with resources needs a robust, evidence-based case. That is how the Poppy project for trafficked women got started: trafficked women were being deposited on their doorstep (because their parent organisation Eaves provides housing for other vulnerable women) and there was no expertise or funding to deal with them. There is a snide attempt to discredit Poppy by implying that their Home Office funding gives them a vested interest in inflating the figures. However, Poppy's 25 bed spaces has recently been upgraded to 54, and they still have to turn women away.

Demolishing police figures does not prove that trafficking into the sex trade is so minuscule that it doesn't matter. Come on Nick. You can do better than that.