The unnamed girl was brought to the UK from Somalia with the intention of removing her organs and selling them on to those desperate for a transplant.
Child protection charities warned that the case was unlikely to be an isolated incident as traffickers were likely to have smuggled a group of children into the country.
The case emerged in a government report which showed that the number of human trafficking victims in the UK has risen by more than 50 per cent last year and reached record levels.
A total of 371 children were exploited, with the majority of them being used as slaves or sexually abused. They included 95 children from Vietnam, 67 from Nigeria and 25 from China. Others hailed from Romania and Bangladesh.
The figures also detail how 20 British girls have been victims of human trafficking. It comes after a series of court cases in which British girls were raped and exploited by gangs of Asian men.