The UK Human Trafficking Centre (UKHTC) said 2255 potential victims of human trafficking were recorded in 2012, up 9% on the previous year.
Those secretly imported into the country - often against their consent or with coercion - were exploited for labour reasons, while many were sexually abused and sold to bidders.
Around one-quarter (24%) of these potential victims were children, up 12% on the previous year, with most coming from Vietnam, Nigeria and Slovakia, and some victims aged under 10 years.
Romania was the most prevalent country of origin for potential victims of human trafficking, with 272 recorded cases in 2012, up 26% on the previous year.
Poland had 240 people caught up in the illegal practice, up 48%, while 209 made the journey from Nigeria to settle in the UK, a 22% rise.
The UKHTC's report said many Nigerian women trafficked for sexual exploitation had been recruited when their parents died. They reported being taken in by a relative or friend of the family, and offered employment or education opportunities in the UK.
Children trafficked into the UK were often used to help with criminal or sexual exploitation, the report said.