At least 2,600 women have been trafficked into England and Wales and forced to work as prostitutes, according to a snapshot report published today.
Police found 17,000 of the 30,000 women involved in the off-street sex trade are migrants, mostly from China, Thailand and Eastern Europe.
They said at least 2,600 of these were trafficked into the country and made to work as prostitutes, often with threats of violence.
A further 9,600 sex workers at brothels and other premises were considered to be "vulnerable migrants", but researchers could not be sure they had been trafficked.
Some of those forced to sell their bodies are made to pay off bonds of up to £30,000 by criminal gangs responsible for the multi-million pound underground trade.
The figures were contained in a report by the Association of Chief Police Officers (Acpo) and is the first of its kind to reveal the scale of the crime.
It followed a two-year study aimed at improving understanding of the nature and scale of the trafficking of foreign nationals for sex, known as Project Acumen.
Nottinghamshire Deputy Chief Constable Chris Eyre, who is the national lead on migration crime, said the report "shines a light" on the problem.
He said: "Human trafficking for sexual exploitation involves the most extreme abuse of individuals in our communities.
"We recognise that Project Acumen focuses on only one area of trafficking, but it clearly sets out the scale of the problems that those in law enforcement, victim support, social care and border protection, collectively face.
"It provides us with a more sophisticated and nuanced understanding of how migrant women are involved in prostitution, how they are influenced, controlled, coerced, exploited and trafficked.
"The publication of this report represents not the end of the process, but the start."
Mr Eyre added work will continue to shut down trafficking routes and to bring to justice those criminals who profit from exploiting women.
The report, called Setting the Record, was co-ordinated over 12 months by a team in south west England, supported by the Metropolitan Police.
Investigators interviewed more than 200 women to find out more about their circumstances.
They found the sex industry was made up of 6,000 premises where the majority of women were trafficked or were coerced by cultural, financial or other factors.
It found significant regional differences in the number of migrants involved in prostitution, from 96% of prostitutes in London to 32% in Yorkshire and the Humber.
The largest number of brothels was found in London (2,103), followed by Yorkshire and the Humber (534), the South East (426) and the West Midlands (342).
Police admitted the findings were incomplete estimates that may miss brothels that advertised in other languages or only accepted clients by invitation.
They said although some women were subjected to kidnap, rape and imprisonment, others were effectively "self employed".
A large proportion of women trafficked into the country were Chinese and talks were under way with their Government about finding ways of stemming the flow.
Some studies have suggested the 2012 Olympics will fuel a rise in the number of migrant sex workers.
But one senior officer said there had been no noticeable change in the number of prostitutes in the four Olympic boroughs so far.
Immigration Minister Damian Green said: "Human trafficking is a brutal form of organised crime where people are traded as commodities and exploited for profit by criminal gangs.
"Combating trafficking and looking after its victims is a priority for the new Government.
"In order to combat trafficking more effectively we need to understand it better, and Project Acumen marks significant progress.
"Having any number of people trafficked into the UK is unacceptable, therefore it is vital that we use Acumen to re-focus our efforts both at targeting the criminal gangs that trade in this human misery and in helping victims escape and recover from their ordeal."Reuse content