A woman forced to have sex with up to nine men a day while being held captive has revealed the horror of modern slavery in Britain - as the Home Secretary vowed to combat the issue.
Speaking exclusively to Sky News on the eve of a major international anti-slavery conference, Theresa May said more must be done to bring the perpetrators of people-trafficking and modern-day slavery to justice
"There haven't been sufficient prosecutions for trafficking in the past," she said.
"Partly I think that's because of complex legislation, legislation that is in different acts of parliament.
"One of the key things we are doing is clarifying the legislation, bringing it into this single bill."
The Government's modern slavery bill is one of the issues being discussed at an international conference in London, intended to increase cooperation in tackling human trafficking.
And Sky News met one former sex slave who was trapped in a house in west London for five years.
Known as "Blessing", she paid a woman £4,000 to travel from Nigeria to the UK on the promise of a job in nursing.
She and 10 other women made the journey by ship, arriving at Tilbury Docks in Essex before being transferred to the house in Ealing that would be her prison for the next five years.
Ruled by her "agent" - known to the girls as Mama G - those kept in the house were guarded by security men, day and night.
"When our customers came, I would hear Mama G start describing us: the sizes of our breasts, the size of our private parts, how tall we are," Blessing said.
"She would then call your room number and say you have customer ... "
When she tried to question why she was there, Mama G would beat her and burn her legs and chest with an iron - while security guards would warn her of the consequences if she tried to leave.
"They will tell you if you dare do anything, they will shoot you," she said.
"I didn't want to die."
She and six others eventually escaped when a door was left open and the group ran to Ealing Broadway Tube Station and jumped the barriers before boarding a train.
"We just made up our minds: 'If we are going to die, let us die'," she said.
"I came into this country to come and look for a better life. I'm a well brought up woman from a good home. I'm married. I've got my children. I never thought 'I'm going to do prostitution'. It's shameful for me."
Blessing is now being cared for in a safe house run by charity The Medialle Trust.
But critics of the Government's modern slavery bill say not enough is being done to support survivors of trafficking.
Government figures say 2,744 people were trafficked to the UK last year, of which 41%, or 1,128, are known to have been trafficked for the purpose of sexual exploitation.
The Metropolitan Police told Sky News that they rely on members of the public to help identify victims of trafficking, and that in some cases men who paid for sex with prostitutes were so alarmed at the apparent slavery of some that they themselves alerted the police.
Phil Brewer, who leads the Met's Trafficking and Kidnap Unit, said: "One of the biggest problems that we have is that [trafficking] is hidden. It's a hidden crime just because of the way these offences are committed.
"We really don’t know the size of the issue."