Herbal stimulant – already banned in US and most European countries – is to become Class C drug

The home secretary, Theresa May, has defied her own expert advisers and banned qat, a mild herbal stimulant that is traditionally used by Britain's Somali, Yemeni and Ethiopian communities.

May said that it would become a class C drug and warned that since the majority of other northern European countries had already banned the herbit, there was a serious risk that Britain could become a"single, regional hub" for its illegal onward trafficking. She said that the penalties for personal possession would escalate in a similar way to those for cannabis, with a warning issued for a first-time offence, leading to arrest and prosecution for persistent users.

"The government will ban qat so that we can protect vulnerable members of our communities and send a clear message to our international partners and qat smugglers that the UK is serious about stopping the illegal trafficking of qat."

May said that there had been an increasing number of seizures of qat in transit in the UK, en route to the Netherlands, where the drug was banned earlier this year.

"Failure to take decisive action and change the UK's legislative position on qat would place the UK at serious risk of becoming a single, regional hub for the illegal onward trafficking [to northern Europe]," she told MPs.

The home secretary's decision clashes with the expert opinion of her own Advisory Council on the Misuse of Drugs (ACMD), which has said there is insufficient evidence to indicate that chewing qat causes health problems, or wider problems in society, to justify imposing a ban in Britain.

Her advisers also said that they had found no evidence to indicate that the trade was linked to organised crime, or used to fund the Somalia-based Islamist group al-Shabab, as has been alleged. Their inquiry also found that there was little evidence to suggest that Heathrow was becoming a European hub for the re-export of the stimulant.

Prof Les Iversen, chairman of the ACMD, reacted to May's decision by sayingsaid: "The ACMD considers evidence of harm associated with the use of qat to be insufficient to justify its control under the Misuse of Drugs Act 1971.

"While I am disappointed that the home secretary has not accepted the ACMD's recommendation that qat should retain its legal status and not be controlled under the Misuse of Drugs Act 1971, I recognise that there are broader policy considerations the home secretary has to take into account and the decision whether to control a substance ultimately lies with the government."The home secretary was careful to acknowledge that the ACMD had undertaken a "thorough and comprehensive scientific review" but said it found a lack of robust evidence in a number of areas.

"The decision to bring qat under control is finely balanced and takes into account the expert scientific advice and these broader concerns," she said.

Opponents of a ban say that it could criminalise as many as 90,000 members of the British Somali, Yemeni and Ethiopian communities, for whom chewing qat is a traditional part of their social lives.

May's decision represents the first major clash between the government and the ACMD since Prof David Nutt was sacked as its chairman in a row with by Alan Johnson, then the home secretary, over the classification of ecstasy.

Nutt said: "Banning qat shows contempt for reason and evidence, disregard for the sincere efforts of the ACMD, and most of all, indifference to the welfare and rights of the communities in which qat is used. Twice in a decade the government's expert advisers published reviews showing that the relatively low harms associated with qat can not justify criminalisation," he said, claiming that persistent US pressure lay behind the move.

Nutt added that the ACMD had proposed ways of minimising the harms caused by the drug. He said ministers, having made negligible efforts to work with the communities involved, could not now claim to have run out of options to help the affected communities in ways that did not involve locking people up.

Some members of the Somali community have urged the home secretary to ban the herb. Mohamed Ibrahim, the chair of the London Somali youth forum, said that chewing qat was no longer confined to the older generation and there was a growing and alarming number of young Somalis among users and that their health and prospects were affected. Some were languishing in mental health institutions or "wasted in the wilderness of benefit dependency".

The drug is already banned in the US and most European countries. including France, Germany, the Netherlands and Ireland.

Qat is imported from Kenya, Ethiopia and Yemen on regular flights to Heathrow but has to be distributed rapidly as it has a lifespan of only 48 hours. It is sold in small shops and cafes in bundles costing £3 to £6 each.

The ACMD report described it as a herbal product made up of the leaves and shoots of the shrub Catha edulis, which releases a mild stimulant after being chewed for about an hour and three quarters.

Imports stood at around 2,560 tonnes in 2011-12, were valued at £13.8m and yielded VAT receipts of £2.8m.

The experts said its use in Britain had declined over the past seven years despite media claims to the contrary. Generally it is chewed at social events in family homes, at community parties or at legal qat cafes. Kenyan qat sells at £3 a bundle with most users typically chewing one to two bundles in an average session lasting perhaps four to six hours.

The ACMD said that while in Africa qat was often used by students, farmers and lorry drivers to stay awake and keep working, in the British Somali community its use was mainly recreational. They said the long hours spent chewing could become a barrier to getting a job but said it was not a cause of unemployment. They noted that the majority of users moderated their consumption to fit their work pattern.