HOWEVER Avdedon asked me to post a couple of links so that she doesn't have to go looking for them. There's Nick Davies' piece here and an attempted rebuttal of it by Rahila Gupta on Comment Is Free.
Nobody is arguing that the trafficking of sex workers does not happen, or that it is in any way other than a very bad thing indeed. What Davies is arguing is that it does no one any favours to trade in statistics so dodgy that they might as well be called lies, and basing a call for new laws on them. This becomes especially worrying when Government are funding NGOs, which come up with research that lets Government do what individual ministers are minded to do, ministers who then get praised in newspapers by journalists with strong links with those NGOs.
Dodgy dossiers and the culture surrounding them gave us the Iraq war and the war on some drugs. They are an intrinsically bad thing even when the cause they support is one to which people are sympathetic for good reasons.