Sex is being sold in London brothels for as little as £15 and a number of premises are offering "very young girls" to customers.
These shocking findings have come from a survey by trafficked women's charity Eave's Poppy Project. It says many of London's 921 brothels go under the guise of massage parlours and saunas.
Co-author of the report, Julie Bindel says: "The police are not resourced to monitor these places. They're not really that hidden because we found them so easily.
"During our research one policeman told me 'We daren't pick up the rock - because we won't know what to do with what might crawl out from under it.'
"Under that rock is illegality on a massive scale: sexual abuse, physical abuse, trafficking and links to other crimes like drug, gun crime child abuse.
"There's no question that there are underage girls working in brothels. There are many men who actively seek sex with underage girls. Some will be trafficked some will be home grown."
Solely using adverts placed in local newspapers, researchers posing as potential sex buyers found high risk services - such as unprotected anal sex - available for as little as 10 pounds extra.
Julie Bindel: "If we tackle prostitution it will make women safer. Prostitution effects all women in denigrates our status - if you can buy and sell a woman you can't have equality."
Brothels were identified in each of London's 33 boroughs, with an average of 28 per borough, ranging from 71 (Westminster) to 8 (Southwark).
Given that only newspaper advertisements were used as source information (as opposed to websites or phone cards) it can be assumed that the numbers in the report represent the tiniest tip of a very large iceberg.
It's estimated that between £50-130m is generated for brothels through illegal newspaper ads alone.