The government still hasn’t got the message. On Wednesday I saw that Theresa May has decided to ban khat, a herbal stimulant popular among Somali, Yemeni and Ethiopian communities. This goes against advice from the government’s own Advisory Council on the Misuse of Drugs (ACMD), which claimed there was “insufficient evidence” that khat caused health problems.

I agree with the ACMD that khat should remain legal, but for different reasons. The legal status of recreational drugs should not be decided by their healthiness. They should all be legal. Individuals should be free to harm their own bodies if they wish to do so. The government should be limited to providing information about the risks, providing customer protection through licensing and quality control, and helping those who struggle with addiction.

With this new ban, khat will go the way of other recreational drugs. Where there is demand, there will be a supply, regardless of the government’s ban. People who want to buy khat will now have to go through the black market. They will become involved with drug dealers who they would otherwise have no business with. These dealers will be unregulated, of course, so there will be none of the customer protection found in a legal market.

The BBC report says: "Somali groups in the UK had told the ACMD that use of khat was a 'significant social problem' and said it caused medical issues and family breakdowns."

Banning khat will likely exacerbate this problem. People whose khat habit is causing a problem will be less likely to seek help, for fear of being branded a criminal and punished by the state. The real problem is pushing the drug business underground. Dealers are risking years in jail for responding to a legitimate demand, so the incentive to obey other aspects of the law is limited and some have no qualms about cutting the drugs with more harmful substances, or assaulting their customers to keep them obedient.

These dealers would not exist if drugs were legal. I realise that while cigarettes are still legal, there is a significant black market in them. This is mostly due to the huge taxes the government hits them with: 82% of the price of a packet of fags is tax. But when recreational drug users can only get their highs illegally, the black market is much bigger. As ever, the example of alcohol prohibition 1920s USA is illustrative.

Finally, legalising recreational drugs would help the government’s finances as well: the tax revenues would be huge. In 2011/12, the government received £2.8m through taxing khat. That was £13.8m worth of khat – the overall drugs market is estimated at between £2.15bn and £6.54bn. But instead, the government ignores advice it has requested, as it did in the case of ACMD chairman David Nutt in 2009. Nutt himself uses a clever analogy to refute the khat ban. But it seems that the state’s illogical control freak attitude will stubbornly persist.

The government should legalise not only khat, but all other recreational drugs. This would correct the current infringement on liberty, make it easier for addicts to get help, bring in tax revenue, and destroy the black market and related crime.