I was wrong about child trafficking from abroad.
It is mostly from SE Asia though, and not all are trafficked for sex.
BBC.
There is currently no official figure for the number of victims trafficked into the country each year.

However, the report said 712 adult victims and 234 child victims were reported last year to the National Referral Mechanism, the official body that identifies and looks after those caught up in trafficking.

Of the victims referred in 2010, 524 were adults and 186 were children.

It is thought the increase could be explained by improvements in identifying victims, although campaigners say the figures of those being trafficked could be far higher as many victims choose not to come forward for fear of being deported.

The report suggested an increase in the number of children being forced into crime, including street begging.

The Child Exploitation and Online Protection Centre estimates there are about 300 child trafficking victims in the UK every year.