Newspaper editors across London have received a letter from the police warning them to stop running advertisements for sex establishments which may involve trafficked women.

It warns editors that they could be held criminally liable if they run ads which turn out to be linked to human trafficking, exploitation or proceeds of crime.

The letter was sent to more than 170 editors yesterday afternoon and asks them to support the police initiative.

The letter from Detective Chief Superintendent Richard Martin, head of the Human Exploitation and Organised Crime Unit, reads: "Advertising in newspapers can play a key role in facilitating the exploitation of trafficked victims. The adverts in question often purport to be massage parlours, saunas or escort agencies, but are in reality a front for criminal networks to advertise trafficked victims for sexual services."

DCS Martin asks editors to put in place a system to make sure they do not accept adverts which are “fronts for criminal networks to advertise trafficked victims for sexual services”.

He warns: “As you will appreciate, criminal liability can arise in certain circumstances where evidence clearly shows that the advertising in question supports or promotes offences associated to trafficking, exploitation or proceeds of crime.”

In October the Croydon Guardian exclusively revealed police plans to get editors and publishers to stop running adverts for massage parlours which often turn out to be fronts for illegal brothels.

Earlier this week we revealed police plans to write to editors asking them to drop the adverts.

In 2008, Newsquest, which runs these websites, became convinced of the link between these adverts and women being trafficked into the country to be used as sex slaves.

The company decided the only way to make sure it did not publish adverts for brothels containing trafficked women was to drop all sex ads from the pages of all of its publications.

Click here to read the letter in full