By Angus Crawford
Home affairs reporter, BBC News
Children trafficked into the UK are being taken from local authority care to work as prostitutes or as child labour, a charity has warned.
Unicef wants safe houses to be provided for trafficked children
The United Nations children's charity, Unicef, told the BBC more than half of those smuggled into Britain go missing.
It says criminal gangs are taking young people from care for exploitation and called on ministers to provide safe houses to protect them from abusers.
The government says it is committed to tackling child trafficking.
The UK's only secure accommodation designed to protect trafficked children closed four years ago.
Recent research showed that out of hundreds of young people brought into this country against their will, more than half had disappeared.
"Fear, deprivation, hunger, being beaten, being sexually abused... we suspect there are thousands," said David Bull, executive director of Unicef UK.
"For a child to be brought to the UK for purposes of exploitation is the most horrendous experience imaginable."
Many are intercepted by the authorities and taken into care, he said.
But he added: "Of the hundreds that have been identified, a majority disappear... into gross exploitation."
Recent research by the government's Child Exploitation and Online Protection Centre (CEOP) found that out of 330 cases of children it believed to have been trafficked into the country, 183 were missing.
There are no safe houses providing 24-hour care and protection in the UK and many trafficked children end up in foster care, bed and breakfast accommodation or hostels.
They remain vulnerable to traffickers, who threaten them and force them to leave.
Mr Bull believes the government has a duty under the Council of Europe convention against trafficking to provide better facilities, such as safe houses.
"It's specialised, with trained carers - they need 24/7 supervision, in a secret location," he said.
"The consequence of not doing that is these children disappearing... into terrible situations of suffering and exploitation."
Breaking the link
The CEOP report showed that the biggest source country for trafficked children was China.
Of the 72 children of Chinese origin identified, the vast majority were missing.
But Edmond Yeo, from London's Chinese Information and Advice Centre, believes many may be from countries such as Vietnam or Cambodia.
However, he feels safe houses would break the link between trafficker and child.
"It would give them that safety net... to cut them off from the people who've engineered the trafficking.
"It's the first step in ensuring our duty to protect them," he said.
Trafficking people for use in the sex trade became a criminal offence in 2003.
The Home Office says it takes the problem seriously.
It paid for the CEOP research and launched an action plan on tackling human trafficking in March this year.
It also signed the Council of Europe convention on the trade.
A spokesman for the Home Office said it applauded Unicef's efforts towards ending human trafficking and protecting vulnerable children.
But it did not believe safe houses for child victims of trafficking were a guarantee that a child would not disappear, he said.
"Children who have been trafficked and who are separated from their parents enjoy exactly the same rights, entitlements and benefits from our child care system as do UK-born children.
"UK law does not allow children to be detained in a secure environment other than in extreme circumstances."
The spokesman added that the government was aiming to provide a safe environment for young people who have been trafficked through a range of specialist support.