"Some have considered large-scale cannabis cultivation as an almost 'victimless crime' but the reality is that vulnerable young people are being exploited," said Martin Barnes, head of think tank Drugscope.

"Unfortunately they find themselves victims twice over –- both at the hands of the criminal gangs who brought them to this country, forcing them to work in cramped, dangerous conditions to fuel the illegal drug trade -- and again when they find themselves treated as criminals by the UK authorities."

A recent Home Office report into child trafficking identified 'Vietnamese young people as a vulnerable group who had been particularly exploited in cannabis production.'

The report went on to recommend that the Crown Prosecution Service should 'avoid prosecuting trafficked cannabis farmers.'

Such sentiments were backed by the Director of Public Prosecutions, Sir Ken Macdonald, when he told an All Party Parliamentary group on child trafficking that he would be 'warning prosecutors to take into account the back story of children found working in cannabis factories.'

As yet, no formal guidance has been issued to courts about how to treat such cases -- such as one pending case involving a trafficked 14-year-old girl charged with cultivation.

"DrugScope urges the Home Office to issue formal guidance as soon as possible to the UK courts," said Barnes.

"These children should not be serving jail terms -– they should be given support and protection."