A new report says that a large number of brothels in London offer full sex for as little as 15 pounds and employ women from more than 75 different nationalities.
In a bid to make the findings, researchers from the Poppy Project, which campaigns against the trafficking of women, acted as clients looking for sex and telephoned adverts listed in local newspapers.
The research team found 921 operational brothels across the capital, offering full sex for between 15 and 250 pounds.
The charity said the full scale of prostitution was likely to be much larger as the survey did not cover adverts placed on cards in telephone boxes or on websites.
But it estimated that between 50 and 130 million pounds a year was being earned by the brothels identified through newspaper adverts.
When women personally providing sexual services answered the phone they regularly sounded miserable, subdued, tired or exhausted, the researchers reported.
"For most women involved in prostitution, the reality is a cycle of violence and coercion, perpetuated by poverty and inequality," the Mirror quoted Helen Atkins, co-author of a report based on the charity's survey, as saying.