Children - particularly from Vietnam and China - are being trafficked to the UK to work as slaves in illegal cannabis farms.

These 'farms', run by organised crime gangs, are often situated in suburban houses. The children, generally aged between 14 and 16, are smuggled into the country before being locked in the houses to water cannabis plants. They have been found sleeping in cupboards or attics to make more space for plants, and are at constant risk of fire or electrocution due to illegal rewiring of electricity supplies.

Rather than being treated as victims, these children frequently suffer a second ordeal upon discovery by the authorities. A 2007 Home Office report on child trafficking describes how at least four Vietnamese children of the twenty two in the dataset were not identified as victims of trafficking and were arrested for cannabis cultivation.

“If a child is identified in a cannabis factory, then are are in a situation of harm, and are probably being controlled by adults,” says Christine Beddoe, director of the charity End Child Prostitution, Child Pornography and the Trafficking of Children for Sexual Purposes (ECPAT). “Decision making on their treatment should flow from that. Instead, children are seen as criminals.”

An all-party parliamentary group on human trafficking last year established guidelines for the Crown Prosecution Service (CPS) on child trafficking in order to avoid such miscarriages of justice. However, the evidence of numerous court cases since then show a reluctance to put this into action. Twelve trafficked Vietnamese immigrants were tried in a single case last year for conspiracy to produce cannabis, including a 14 year old girl. A 17 year old girl in a separate case will be deported as a foreign criminal at 18.

ECPAT frequently provide expert witnesses for court cases, securing the release of a child earlier this year after the CPS admitted that the conviction was not in the public interest. Such victories are a tough fight: this appeal alone took five months of legal wrangling by a specialist team. The cases continue, despite a landmark ruling in July 2007, when Judge Christopher Mitchell refused to sentence two young Vietnamese men, aged 16 and 20, saying that they were victims of “modern slavery” after reading about cannabis farms in a newspaper.

“There is a gap between the mechanism of protection provided by the CPS guidelines and the reality on the ground, where there is no clear policy or practice guidelines for police to follow,” says Beddoe. “The police and the CPS say that these children are not trafficked, not because there is proof that they are not, but because they haven't investigated the possibility.”

Although these children were identified as a risk group over a year ago, Home Office Minister Alan Campbell admits that “No central records are kept on juvenile offenders who may have been victims of trafficking. It is not therefore possible to give a reliable figure.”

Independent research and uncollated data suggests that the problem is on a huge scale. The charity DrugScope found that in London alone 1500 cannabis farms were raided from 2005 – 7, and that approximately two thirds of these were run by Vietnamese criminal gangs. When farms are raided, police arrest the only people there – the so-called 'gardeners', typically trafficked adults or children.

“Young people who have been trafficked and are found tending cannabis farms should be treated as victims, not criminals,” said Harry Shapiro, director of communications at DrugScope. “They work in cramped, dangerous conditions and should be given support and protection, not imprisonment.”

Tragically, these children can all too easily slip through the net, a lack of co-ordination meaning that they bypass government provisions for lone asylum-seeking children. Local authorities and children's services will deal with the child as a young offender, guilty of cannabis cultivation or of carrying false documents, despite the fact that the UN's Palermo Protocol states that a child cannot consent to his or her own exploitation. Being instantly criminalised means that they are not referred to specialist trafficking units and are left with virtually no ability to claim asylum or protection.

Independent charities and pressure groups, providing much needed research and support to victims and the authorities, are calling for the creation of a Human Traffic Rapporteur, to provide clear information and act as a watchdog for the implementation of laws. This is considered international good practice by the UN, and a successful model is in place in the Netherlands.

The deadline for ratifying the Council of Europe Convention on Action against the Trafficking in Human Beings is approaching. It requires member states to regularly gather and analyse information on human trafficking, and includes measures for victims to claim asylum. However, no concrete policy plans have been made as to its implementation in the UK, and it was announced last week that the Met's specialised police unit will close in April.

The child victims of the cannabis trade may have a long wait before they gain automatic protection.