The ban on Khat is irrational and preposterous

There is no longer any pretence of reason to our drug laws. Today, the Home Office announced Khat, a herbal stimulant popular in the Somali community, is going to be banned. This is despite the fact that the Home Office itself believes it causes little harm to users or society.

A 2011 report from the Home Office said there was "a general lack of robust evidence on the link between khat use and social harms". Reports of harm to the Somali community were based on "often contradictory anecdotal statements".

Legislation against the drug in Europe and north Africa, it said, "had little success in curbing demand and has taken place with little consideration of evidence".

It's not just the Home Office. The World Health Organisation itself accepts that khat is not a "seriously addictive drug".

The home secretary's own drug advisers – the Advisory Council on the Misuse of Drugs (ACMD) – recommended against prohibition.

"In summary, the evidence shows that khat has no direct causal link to adverse medical effects," its report from earlier this year found.

"On the basis of the available evidence, the overwhelming majority of council members consider that khat should not be controlled under the Misuse of Drugs Act 1971. The ACMD considers that the evidence of harms associated with the use of khat is insufficient to justify control and it would be inappropriate and disproportionate to classify khat."

They really couldn't have been clearer.

Home Office sources suggest the move is motivated by concerns around the trade route the drug enjoys on its way from north Africa to London. About 2,500 tonnes of khat, worth about £13.8 million, were imported to Britain in 2011/12, bringing in £2.8 million to the HMRC.

Prohibition is the most foolish possible response. All the data on drug use shows than a ban does not eliminate demand, it merely forces the product underground. The home secretary has encouraged a black market flowing from north Africa to Britain.

The Home Office says the decision was also motivated by the fact that police were finding the drug in London before it made its way to other European states, where it is banned.

This is irrelevant. They decided to ban it, against the evidence. It is not our responsibility to assist in the legislative idiocy of other nation states. We have quite enough legislative idiocy of our own to deal with.

The drug itself has been in use for thousands of years in the Horn of Africa and the Arabian Peninsula. It's particularly popular in Yemen, where users chew on it for several hours, often forming tennis-ball-sized clumps of it in their cheeks as they chat.

The effects are standard for a stimulant. It induces a state of mild euphoria and increased alertness, often characterised by a flight of ideas. The end of a session can leave users feeling irritable and moody and they are typically lethargic the following day. It's like a very mild form of amphetamine.

As far as we can tell it is doing very little harm (certainly less than alcohol or tobacco) to the users who take it. There is no evidence of a broader social harm. And the trade route through which it arrives in the UK would be better monitored by being kept above board rather than pushed toward the black market.

But that makes no difference. UK drug policy is not, and can lay no claim to be, inspired by reason. It is now as logically and scientifically valid as witchcraft. Theresa May's decision was entirely predictable and preposterous.