Police have been accused by a senior MP of "cosying up" to "pimping websites" that she claims allow trafficked women to be "raped multiple times a day".
Dame Diana Johnson said it was "disgraceful" that police forces and the National Crime Agency (NCA) were engaging with businesses such as Vivastreet.
Struggling crimefighting chiefs were today unable to tell a cross-party committee of MPs whether any prosecutions had stemmed from working alongside such sites to gather intelligence of traffickers.
In a blistering exchange Dame Diana told a boss at the NCA: "You're pursuing a strategy that seems to me to be cosying up and enabling adult service websites to carry on allowing trafficked women to be raped multiple times a day. I think it's disgraceful."
She voiced her anger after the Government confirmed Home Office officials attended an online Adult Services Websites (ASWs) industry event, jointly organised with the National Crime Agency, last summer.
Dame Diana claimed sites such as Vivastreet - which was represented at the event - are "pimping websites" known to trade in trafficked women, and questioned why law enforcers are not being tougher. Dame Diana told representatives from the police, National Crime Agency and the Crown Prosecution Service: "Criminal acts are taking place in plain sight. You're having people from these adult service websites talk to your police officers, attend conferences and give a veneer that they're working collaboratively with you.
"I'm really concerned that in plain sight their business model is a pimping website."
Addressing last summer's conference she said: "There was someone who was convicted as a trafficker, he was given an account by Vivastreet. A representative from that website was invited by the NCA to speak at a conference co-hosted by police.... You're having people that enable trafficking to your conference, and you're saying that's ok."
She said the fact that multiple adverts on Vivastreet and similar sites are linked to the same phone numbers are "red flags" that pimps are using them to sell sex with victims of trafficking.
But Rob Jones, director of threat leadership at the NCA, and director general of the National Economic Crime Centre, said the relationships were vital for harvesting information about traffickers. But officials were unable to say how many prosecutions had been carried out as a result, and how many victims had been saved.
He told the Home Affairs Select Committee: "It's not a policy decision to cosy up to any of these companies."
Mr Jones said that simply shutting down such sites would drive them onto other encrypted networks, adding: "We haven't cosied up to anyone, there's a real tension and we welcome legislation to bring these companies to justice, that's what we need."
He said that if there is any evidence of individuals being involved in trafficking, these would be investigated.
Dame Diana asked how many prosecutions had resulted from working with adult services websites.
Lynette Woodrow, lead for modern slavery at the CPS, said she was unable to provide precise data, while Mr Street said several victims of child sex abuse had been identified and saved. Dame Diana said: "I don't know if the policy you're pursuing is working. I want hard data."
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