TONIGHT a TV investigation will reveal the truth behind a murky Cheltenham underworld linked to a network of brothels across the UK.

Gloucestershire police coordinated the country's biggest ever strike against people trafficking – leading to dozens of criminal convictions.

In The Hunt for Britain's Sex Traffickers, a Channel 4 documentary screened over the next three nights, camera crews followed officers as they tracked down the masterminds behind the multi-million pound trade.

The programme includes interviews with women brought to the county to work as prostitutes and often forced to have sex with up to 10 clients a day.

Det Supt Alex Drummond, of Gloucestershire police, who played a key role in the operation, spoke to the Echo about the pioneering operation, which changed the way police dealt with vice crime forever.

He said: "In terms of scale, it was bigger than anything we have done before or since.

"With some 52 forces across the country taking part, it was a massive project which I am proud to have been part of.

"It completely changed our understanding of vice crime.

"Prior to the operation, people running brothels may have thought they could escape under the radar, especially in a well-to-do town like Cheltenham.

"But now they know we have the resources to track them down. If they are breaking the law and making life a misery for others, they will be treated just like any other criminal."

Dubbed Operation Pentameter II, the coordinated swoops resulted in 528 arrests across the country.

They uncovered 167 victims, many of whom were trafficked into the country from China and eastern Europe.

Armed units burst into more than 800 premises, many of them massage parlours and saunas, recovering victims as young as 14 and seizing more than £500,000 in assets.

In Cheltenham, a team dedicated more than 18 months to bringing down the crime ring.

As many as 100 officers were drafted in to spring raids at brothels in Evesham Road, Normal Terrace and London Road.

Mr Drummond said: "Raids across the country were coordinated simultaneously from Gloucestershire.

"We wanted to carry out the strikes at the same time so we would stop branches of the criminal network from suspecting we were on to them.

"But throughout the operation we had to balance the need for covert intelligence gathering with the need to protect the women being exploited.

"The girls being forced to work in the sex trade were often in an extremely vulnerable state, so their safety was an important factor."

The operation began with months of intelligence gathering, enabling officers to build up a picture of the town's vice scene before working their way up the criminal chain.

They uncovered an underground network spanning towns across the UK, for which girls were moved around like cattle.

"It was a bit like turning over a stone," Mr Drummond said. "We knew if we looked underneath it we would have to be bold enough to deal with whatever we discovered.

"What we found were highly organised criminal organisations operating in franchise-like businesses across the country.

"In some cases women were brought over to the UK under the illusion they were going to work as cleaners or housekeepers. But they had their passports taken off them and were told they owed a debt to their employers.

"None of the girls we spoke to wanted to be involved in prostitution. They had been forced into it."

In hard-hitting footage due to be screened in the documentary, one prostitute says she was traded "like a pig or a dog" as a criminal organisation bid £30,000 for her services.

She said she did not see any of the money however, with crime bosses racking up a small fortune in profits.

Ultimately it was the money laundering behind the brothels which led to many criminal convictions.

By tracing the bank account details of brothel managers, police were able to pinpoint exactly who was profiting from the enterprise.

Several convictions were made linked to brothels in Cheltenham, with thousands of pounds recovered.

Police worked with social services to support girls being exploited in the town, helping them to return to their country of origin.

Tim Brain, the county's former chief constable, described Operation Pentameter II as one of the proudest achievements of his career.

Mr Brain, who took a leading role in shaping Government policy towards vice crime, said the raids marked a change in attitudes towards prostitution.

"Any man who intends to pay for sex with a prostitute will have to think very carefully," he warned at the time.

"It will be no defence in future to claim they did not know someone was trafficked or controlled by someone else for gain."

The Hunt for Britain's Sex Traffickers will be screened at 9pm over three nights – tonight, tomorrow and on Thursday.

TIMELINE:

- June 2007: Operation Pentameter II was launched following Pentameter I – a smaller scale operation to combat human trafficking. Officers began compiling evidence of Cheltenham brothels.

- December 2007: Gloucest-police smashed a sex den racket in a series of daylight raids in Cheltenham at addresses in Pittville, St Paul’s and the town centre.

- February 2008: A brothel in Evesham Road was raided for the second time in two months with armed officers storming the building.

- May 2008: Police swooped on a suspected brothel in London Road arresting three people.

- June 2008: Police launched a second swoop on the London Road flat and arrested three people on suspicion of running a prostitution ring.

- September 2008: Operation Pentameter II draws to an end. The ring running brothels has been cracked.

- August 2010: Police swoop on a flat in London Road, arresting three women on suspicion of running a brothel.

Six convictions were made in Cheltenham following arrests in Operation Pentameter II:

- Siufan Cheung, 44, from Moreton-in-Marsh. was arrested in connection with a brothel raid at Evesham Road. On February 25 she was sentenced to 12 months in prison for assisting in the management of a brothel and 12 months for offences under the Proceeds of Crime Act.

- Greig Blackhorse, 42, of St Paul’s Lane, Cheltenham, was arrested in connection with a brothel raid at Normal Terrace. On August 18 last year he was sentenced to eight months in prison for brothel management and forced to forfeit £10,555 in cash.

- Jackie Khan, 60, from Borehamwood in Hertfordshire, was arrested in connection with a raid at Normal Terrace. In January, he was sentenced to two-and-a-half years in prison for money laundering, management of a brothel and possession of cannabis.

- Ling San-Wong, 41, was arrested in a brothel raid at Normal Terrace. Charged with money laundering and management of a brothel, she was sentenced to 10 months imprisonment and ordered to forfeit £3,751.

- Kang Dong, 50, of London Road, Cheltenham, was sentenced on October 3, 2008 to six months’ imprisonment for money laundering and brothel management.

- Dao Honk Xu, 52, was arrested at London Road and sentenced on January 15 last year to two years and nine months in prison for management of a brothel and offences under the Proceeds of Crime Act.