They drove north during the night, up from Nice, through the Channel Tunnel and into London. Abina remembers stopping outside a tower block, her boyfriend guiding her into a tiny flat and then a back room where she was locked inside.

The first British man to rape her arrived the following morning in mid-December 2009, the next that afternoon.

The only time she was allowed to leave the room was to use the shower or the toilet next door. She had no phone, no television; food was brought to her room by her boyfriend.

Abina, 26, from Ghana, says she could do nothing but wait, "miserable", for the next man. "It was my first time to England, my boyfriend said it was East London but I have no idea. I never ever went outside. There was a street below but the window was locked."

For more than 300 days Abina was incarcerated in the apartment, during which hundreds of men visited, some black, some Asian, most white, and paid her boyfriend £30 ($62) to have sex with her. Men were allowed to beat her, she says, but most were not as aggressive as her boyfriend.

He told visitors that they need not use a condom, and when she became pregnant he punched her so hard Abina lost her baby.

Not all the women trafficked into Britain are for sex. Gloria was 9 when she was exported as a domestic slave from Nigeria to Italy through friends of her father's. After seven years of unpaid household chores, she was flown to Manchester in March 2006 and forced into a life of domestic servitude with another family.

Imprisoned in their home, aged 16, she was coerced into caring for five children and doing all household chores. She worked 20-hour days without receiving a penny; she slept on the living room floor and was never allowed outside unattended. Then the beatings began.

"You had to do whatever they ask. They shout, blaming you for everything, some time they bit me, they beat me. They say you are just a slave, you don't say anything, even though I am a child myself. I was scared all the time."

Abina and Gloria are two of the thousands of women trafficked into the UK, victims of a crime that stirs revulsion and controversy like few others.

This weekend marks the 224th anniversary of the inaugural meeting of the anti-slavery movement in London, the city where Abina was enslaved most of last year. Now Timothy Brain, the UK's most senior police officer dealing with human trafficking before his recent retirement, has decided to speak out about his mounting frustration over government policy on the issue, as well as the abhorrent nature of the crime.

"We think back to the cotton plantations and sugar plantations of the 18th and 19th century and it wouldn't be as bad as what some victims go through. It's inhumane."

The Government has vowed repeatedly to take the issue seriously.

Immigration Minister Damian Green said: "It is simply intolerable that in 2011 human trafficking still plagues this country." Yet concern is mounting that the systems put in place to help victims and target traffickers are being systematically dismantled by the coalition.

Abina escaped last October. As always, she tried the apartment door when her boyfriend left; this time, he had neglected to lock it. She recalls panicking, opening the drawer where he stashed the money she made, taking the £30 from her last client and running into the street.

"I was terrified. I ran towards a train station and saw a couple, and I say I need to get out of here." The couple took her to Victoria coach station and bought her a ticket to a northern city. There, a woman found her weeping in the city centre and took her in. Within weeks Abina had found a job, selling perfume for tips in the lavatory of a well-known nightclub in the city.

"I was so happy not working as a prostitute," she smiled last week, recalling her escape and rubbing her neck, which clients used to grip so hard it bruised.

But her fortunes soon changed again. Last November, police raided the club. Abina was arrested as an illegal immigrant and sent to Yarl's Wood detention centre near Heathrow Airport for deportation. Four weeks later a charity assessed her, identified her as a trafficking victim, prevented her deportation and is now helping her rebuild her life.

Gloria, too, made a break for it one afternoon. She fled from the home in March last year, telling staff at a college nearby that her life was in danger. "I couldn't go back, it would only get worse," she said.

Although police arrested her captors, the case was dropped for insufficient evidence. Locating trafficking victims is notoriously difficult; most cases emerge through a network of voluntary groups or occasional police raids on known brothels. But now Brain believes that momentum is being lost. Initially police were behind the UK Human Trafficking Centre, a pioneering facility that pulled together intelligence, police and immigration experts.

The centre closed in Sheffield in April last year, moving to the Serious Organised Crime Agency (Soca), and since then sources say 90 per cent of its specialist staff have left. Soca itself is now to be wound up and assimilated into the new National Crime Agency.

Brain believes the relegation of the trafficking centre to an undefined role within a new organisation betrays a shifting of priorities: "The net result is that it is just going lower and lower down someone else's policy agenda," said the former chief constable.

With the resignation of the Human Trafficking Centre's head, former Detective Chief Superintendent Nick Kinsella, anti-trafficking policing has lost a recognisable national co-ordinator. When Soca was asked who now headed its anti-trafficking team, its press office could not recall the incumbent's surname.

Concern is mounting that an apparent lack of proactive policing has bolstered Britain's reputation as a soft touch for traffickers. Government sources cite a lack of frontline police officers trained to identify trafficked people, especially women, who are often too terrified to approach police and testify against their captors.

Kinsella's ambition was for every frontline police officer to understand the impact trafficking had on its victims and to treat such women as victims rather than illegal immigrants, but he believes this is not happening.

Convictions for trafficking, by comparison with narcotics crime, are desperately low. Abina's traffickers were never arrested because of difficulties trying to identify the correct address. On average there have been 25 convictions for sex trafficking a year since 2004, with only eight in England last year. Scotland and Wales have yet to record a single successful prosecution.

The consensus among the voluntary sector is that trafficking's political profile has slipped. Incentives to tackle it are few, as it is an invisible crime largely below the electorate's radar. Brain said trafficking's underground nature helped explain its position as "peripheral to what most Home Office and police strategists see as core business".

Anthony Steen, chairman of the Human Trafficking Foundation, said: "In William Wilberforce's day, slavery could be seen. Now it is hidden from view but no less prevalent."

Another factor influencing the allocation of resources to combat trafficking is quantifying the numbers.

Data gathered under Operation Acumen, an intelligence exercise by senior police officers, indicated that up to 11,800 women may have been trafficked into England and Wales. Peter Bone, chairman of the all-party parliamentary group for human trafficking, estimates there are at least 10,000 slaves in the UK, and says: "If hardened police officers say this is happening on the scale they say, and I'm a rightwing Tory arguing to opt into an EU directive [on trafficking], that indicates it is pretty serious."

Abina's experiences are similar to those of Morowa, 33, who landed in London from Ghana in April 2003 expecting to receive help with her education from friends of her father. They collected her at Heathrow and drove for several hours to a "small village" where they said she was welcome to stay.

Morowa was kept imprisoned for almost four years, again locked in a modest room where hundreds of men arrived to abuse her. She has no idea where all the men came from, or how much they paid, because she never received a penny.

Many trafficking experts condemn Britain's failure properly to care for those who have escaped.

Britain purports to be a world leader in fighting human trafficking; now, they say, is the time to prove it.

The numbers

Police intelligence collated for Operation Acumen, the most authoritative effort to determine the scale of sex trafficking in England and Wales, identified

migrant women trafficked for the sex trade

vulnerable women who might include trafficking victims

men a day - and possibly up to 30 - visit each trafficked woman forced into prostitution