The two women were frightened and nervous, regarding their would-be rescuers with suspicion.

They insisted that they were all right. They wanted to work as prostitutes. They had college fees to pay back in Lithuania and this was good money, easy money.

Looking around the house, a sizeable 1930s semi in a quiet street in a small British city, the police officers were not so sure. The rooms were dirty, there was hardcore pornographic material lying about and scorched sheets of foil – a telltale sign of heroin use.

A few minutes later, when she was alone, the older of the two women approached one of the officers. She was 21 and desperate for help. She said she was in debt to a Russian man who ran the brothel and who had threatened to beat her if she tried to escape or spoke to the authorities. To pay off her debt she was having unprotected sex every day with 15 to 30 men.

The young woman’s story is typical of the trafficking victim: lured to Britain by the promises of money and work, passport taken on arrival, sold to a brothel owner for about £2,000, enslaved to pay off that money and controlled by the threat and reality of violence.

What is less expected is that the brothel where she was kept as a sex slave is not in London, Birmingham or one of the metropolitan centres. This brothel was in the cathedral city of Peterborough and is one of 80 that have been raided by Cambridgeshire police this year.

Senior officers have been staggered by the discovery of off-street brothels – “sex prisons” in the words of one detective – in towns such as Wisbech, March, Huntingdon and Cambridge. They believe there are many more operating across the county.

Cambridgeshire is not alone. Around the country police forces are realising that human trafficking, a hugely profitable business run by organised criminal gangs, is no longer a big city problem.

In towns as seemingly unlikely as Cheltenham and Leamington Spa, police have moved to shut down brothels. “If you can find it Cheltenham, you can find it anywhere,” said Tim Brain, Chief Constable of Gloucestershire and a national police spokesman on the issue. “I’m expecting we will uncover a lot more.”

Dr Brain said that the key to defeating the traffickers was to deprive them of the huge profits they were making from the trade in human beings.

“There is significant money being made by criminals here, international money,” he said. “Asset confiscation is a big weapon in our armoury. If we can go after the profits that is what will have a real impact on these people.”

Next week Jacqui Smith, the Home Secretary, will announce formally an antitrafficking operation that will involve every British police force and the Garda Siochana in the Irish Republic.

Pentameter II is an attempt to clamp down on a problem that is perceived to be growing but about which the authorities still know relatively little.

What the police and other law enforcement agencies do know is that they will have to get to grips with a complex, secretive and violent criminal network. “We turned the stone over,” said Detective Chief Superintendent Russell Wate, Cambridgeshire’s head of investigations. “When other people turn it over I suspect they will find the same thing.”

Chief Superintendent Paul Phillipson, the police commander in Peterborough, thought that he knew the city pretty well. He was born and raised there and lives locally. Concerned by scraps of intelligence and reports from neighbourhood officers, Mr Phillipson took a proactive approach. Within months, with the help of the UK Human Trafficking Centre, dozens of suspected brothels had been identified in the city and the operation, codenamed Radium, was spread countywide.

“Two or three years ago Peterborough had one or two saunas which were probably operating as brothels and I’m not even sure we had a branch of Ann Summers,” Mr Phillipson said. “We were hardly the sex industry capital of Britain. But it was happening below the radar, behind closed doors and only ever came to our attention in a minor way with complaints about cars late at night, strange men knocking on doors in residential areas.

“I have been very surprised by what we have found. I would never have thought it was possible for someone to sell a woman. I can’t comprehend the mindset that values a human being so lowly that they treat them as a commodity. That’s slavery.”

Investigations have uncovered evidence of auctions in Peterborough where men – gang bosses and brothel owners – buy and sell women for between £500 and £3,000. The women are then virtual prisoners in rented houses in residential areas such as New England and Millfield, just north of the city centre. They are afraid to go out and receive none of the money paid by their “clients”.

To keep them from meeting neighbours or getting to know their surroundings, the brothel owners frequently move them from one rented house to another. Advertising is through the “personal services” columns of newspapers and internet sex sites. The ads talk of “dreamgirls”, “beautiful young European girls” and “ladies new to the area” and give mobile telephone numbers.

Two “dreamgirls” escaped this year from a house in Northfield Road, one running to the police, the other to an immigration advice centre. Six more women were “rescued” in police raids. A 16-year-old trafficking victim was driven to the centre of Peterborough and dumped on the street after her pimp discovered that she was pregnant.

Another woman rescued from a brothel said that security guards at the house showed her a sword and baseball bat and said she would be beaten and stabbed if she tried to escape.

Mr Wate said: “Many of the women we found were simply too terrified to talk to us. Very few were prepared to say they were being held against their will. They’ve been threatened.”

In this climate of fear, detectives face a huge problem amassing evidence and persuading victims to give evidence against those who run the brothels.

Despite all the raids in Cambridgeshire, only one man has been charged under trafficking legislation. Operation Radium is, however, continuing and the police believe they have identified several criminal gangs.

The police expect little help from the men who use the brothels, most of whom come from the tens of thousands of migrant workers employed in the “picking and packing” industries in Fenland’s fields and food factories.

The increase in sex trafficking appears to have gone hand-in-hand with the surge in immigration in East Anglia that led Cambridgeshire’s Chief Constable, Julie Spence, to demand more money to police a rapidly increasing population. Last week Mrs Spence said that ministers were not taking account of the effect that a rise in immigration was having on policing. She said Cambridgeshire had become a staging post for immigrants, partly because farm work was readily available.

Mrs Spence said the effect of immigration growth seeped into all areas of policing. Foreigners got into difficulties because they were unfamiliar with traffic laws; investigations into crime could involve trips abroad to interview relatives; police had also noticed a growth in prostitution, driven by the influx of large numbers of single men. She said bills for interpreters employed to help police to process suspects and question witnesses had shot up.

In Peterborough, Mr Phillipson fears that local men are among the new sex industry’s customers. “I don’t think this is confined to our new communities,” he said. “My feeling is that there are local men who have been on cheap flights to Tallin, Prague and Budapest and see that paying for sex is regarded more as the norm there and they think they can do it here as well.”

Mr Phillipson intends to prevent the spread of the brothels and the abuse of the women incarcerated in them. “There are no Home Office targets for this kind of police work,” he said.

“This is rape and sexual abuse, happening on a daily basis, but it is unreported crime. I won’t achieve any reduction in crime statistics by closing brothels, I won’t achieve any of my core targets. But, quite frankly, I don’t care. As far as I’m concerned this is what police work is about and I know that it’s the right thing to do.”

The antitrafficking operation has been labour intensive, involving the Cambridgeshire force’s serious and organised crime unit, child protection team and beat officers.

While most of the brothels have been run by Eastern European gangsters, the sweep through the county has also uncovered off-street brothels operated by Chinese snakehead gangs and evidence of African women being trafficked.

The victims’ stories

These are the stories of some of the trafficked women taken out of brothels in Cambridgeshire

Victim A
A 30-year-old Czech woman who was persuaded to come to Britain in August 2006 by the promise of a well-paid job as a waitress. She arrived at a regional airport and was taken to a house in Gloucester where her passport was taken from her, she was beaten and forced to work as a prostitute. She was subsequently sold on to a brothel in London and then auctioned again and found herself in Peterborough. This year she escaped through a bedroom window. She has been helped by the Poppy Project charity to return to the Czech Republic

Victim B
A 21-year-old Gypsy from Slovakia who was taken with a friend to Britain by car and boat by a man who promised her well-paid work as a shop assistant. She told police that after a long car journey in Britain she and her friend were sold for £1,000 to a Middle Eastern male. On her first night in a brothel in Peterborough she was raped and threatened with violence. She was told that she would receive half the money she earned but that the brothel owners would look after the cash until they were ready to let her go. She received £10 per week which then had to be repaid for toiletries and food. In spring 2007 the woman attended a sexual health clinic suffering from an acutely painful pelvic condition. She told staff what was happening to her and they passed details to Cambridgeshire police. A search warrant was executed and two Lithuanian women were arrested on suspicion of managing a brothel. Victim B has since returned to her family in Slovakia

Victim C The woman was afraid that her captors would kill her and her family if they knew that she had talked to police. She had a friend whose back had been broken in a beating by the brothel owners. She said weekend working hours in one brothel where she was held were from 11am to 3am with prices charged at up to £100 per hour. Another woman took £12,000 in three months but was only ever given £10. She tried to hide £250 but was subjected to a beating when it was found

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