The case, involving an unnamed girl, was detailed in a Government report into human trafficking, which claimed that the number of people trafficked in Britain rose by more than half last year.
According to the report, 371 children were exploited, including 95 from Vietnam, 67 from Nigeria and 25 from China.
The girl's organs were intended to be sold to people seeking a transplant, and child protection charities warned the case was unlikely to be an isolated incident.
Bharti Patel, the chief executive of Ecpat UK, a charity which campaigns against child sexual exploitation and trafficking, told The Daily Telegraph: "Traffickers are exploiting the demand for organs and the vulnerability of children. It's unlikely that a trafficker is going to take this risk and bring just one child into the UK. It is likely there was a group."
The details were published on Anti-Slavery Day, as the government announced tough new sentencing plans for traffickers, under which offenders who already have a conviction for a serious sexual or violent offence will get an automatic life sentence.
The measure will be included in the Modern Slavery Bill, which was unveiled by Home Secretary Theresa May at the Conservative Party conference last month.
It will also introduce Trafficking Prevention Orders to restrict the activity and movement of convicted traffickers.
James Brokenshire, crime and security minister, said: "Modern slavery is an appalling evil in our midst."
"All this is a good start, but we need everyone to play a part - government, law enforcement, business, charities - if we are to consign slavery to the history books where it belongs."
And victims' minister Damian Green said: "The trafficking of vulnerable men and women is something that no civilised country should tolerate."
Matthew Reed, chief executive of The Children's Society, welcomed to move, but called for the Government to do more than just toughen up criminal justice measures.
He said: "The announcement of harsh penalties for traffickers is an important step forward, coming as it does on Anti-Slavery Day.
"But for the fight against this brutal crime to be effective, the victims of trafficking must get the support they need to be kept safe.
"Too many trafficked children, who are subjected to a range of horrific abuse, such as domestic servitude and sexual exploitation, are not getting the protection they need to keep them safe from further exploitation and abuse, including being re-trafficked."