The Home Office study also states that cases of human trafficking have risen over the last two to three years.
But Home Office Minister Vernon Coaker says demand for sex with trafficked women is falling.
He told MPs that adverts telling men they could be charged with rape if they pay for sex with a woman working under duress was increasing awareness.
Police behind Operation Pentameter, a four-month crackdown which saved 84 trafficked women from prostitution, have written to men's magazines and distributed leaflets to people going to the World Cup in Germany.
Mr Coaker told Parliament's Joint Committee on Human Rights there was evidence that demand for sex with trafficked women had fallen as a result.
"We think there is evidence of the fact that the punters, on the various websites, that their behaviour has been influenced by these messages that have been going out," he said.
"We know that we need to do more with respect to many of these things. We know there are challenges that we have to meet.
"This is a new area of work - it's something that five, 10 years ago perhaps, people very rarely talked of.
"But it's a major challenge for us and we're determined to do what we can to beat it."