by Alison Holt
Social affairs correspondent, BBC News
Women are tricked into being trafficked into slavery
"Sarah" is giggling into her mobile - she could be any other 21-year-old trying to arrange where to meet her friends, but this sort of freedom is still new for her.
At the age of 12 she was trafficked to the UK into a life of domestic slavery.
"I was told I would have a better life," Sarah tells me quietly. We've changed her name to protect her identity.
She describes how she was taken from school by a stranger and put on a plane from Nigeria to London.
Once in the UK, she was sent to live with a Nigerian family, who expected her to look after their children, as well as cook and clean for them.
For three-and-a-half years she was a virtual prisoner in the house.
"It was more like slavery. I have to clean the house, look after the kids.
"If there was any mistake, or I forgot to do something because I was looking after the baby, I got beaten. I got punished."
Sarah ate different food from the family and slept on the floor in the children's room and only started going out of the house when the eldest child went to nursery.
She was told if anyone speaks to you, just smile. At the age of 18 she managed to get away from the family, but she still worries they will find her.
Many women end up being domestic or sex slaves
A new report, by the children's charity Unicef and the anti-trafficking campaign group Ecpat (End Child Prostitution, Child Pornography and the Trafficking of Children for Sexual Purposes), says there are many other children like Sarah who are forced into domestic slavery, the sex industry or who are used for benefit fraud once they are trafficked into the UK.
Most remain hidden, but government statistics show over an 18-month period 330 children were confirmed or suspected of having been trafficked into the country.
Of those, 183 later disappeared from the care of social services, probably back into the hands of traffickers. The youngest child was nine months old, and no one knows what was planned for that baby.
The head of Unicef UK, David Bull, points to its research which shows even when children are found, the protection they get is inconsistent and in some areas, absent. He says that is not good enough.
'Fear and suffering'
"I think the most devastating statistic is the 180-odd children who have gone missing from social services care.
"We can't allow that to happen because we know what is happening to those children. They're being seriously exploited.
"They're living in fear and suffering and pain and anguish, away from their families and any kind of protection."
The report says there has been significant progress in tackling trafficking, but a lot more needs to be done.
Home Office minister Vernon Coaker says they are determined to combat the problem.
"It's a vile crime, trafficking children for sexual exploitation or for domestic purposes is simply horrific. We're determined to do more. We know we've got to do more, and we will do more."
As for Sarah, she is currently fighting to stay in this country. After nine years she no longer knows where her family is in Nigeria and fears for her safety if she has to return.