Reports in Tuesday’s Guardian were little short of sensational. Cannabis use dramatically improves memory capacity in older brains. German research suggests that small doses of tetrahydrocannabinol (THC) produced “profound, long-lasting improvement in cognitive performance”.

The results indicated that this could possibly stave off dementia for five to 10 years, the reverse of the impact cannabis is known to have on younger brains. Or at least this was the case with mice. As yet, no one knows about humans, but that is good enough for me. I am happy to sign on as a mouse.

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What is absurd is that research into such uses of drugs would in Britain be technically illegal. Such is the hysteria over cannabis that still stalks Whitehall that Britain is among the most backward nations in its intolerance of the herb. At the last count, cannabis has been decriminalised – wholly or in part – in Australia, Canada, Chile, Colombia, Costa Rica, the Czech Republic, Germany, India, Jamaica, Mexico, the Netherlands, Portugal, South Africa, Spain and Uruguay. In Canada, 100,000 patients are registered for medical cannabis, and the drug is about to go wholly legal. In Uruguay it is on government rations.

America four years ago saw poll support for legalising recreational cannabis reach a majority, with overwhelming support for medicinal use. The drug is legally on sale in Republican as well as Democrat states – in Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon and even Washington DC. It has been decriminalised in 21 states and is on sale for medicinal use in 25, reaching a fifth of the population. In Colorado, where sales last year topped $1bn (£800m), $40m in tax receipts were specifically allocated to school building.

Though use of cannabis is still technically a federal offence, the federal drugs administration openly “supports research into the medical use of marijuana and its constituents”, acknowledging its relief of a wide variety of ailments – from epilepsy and multiple sclerosis to cancer. Nobody is going to put the clock back, not even Donald Trump.

Britain loves to criticise foreign countries for their social primitivism. It derides the Irish for banning abortion; it ridicules Gulf states for suppressing alcohol; it formally protests at Nigerian genital mutilation, Saudi isolation of women, and Chechen persecution of gay people. It loves to set the world to rights by its own standards.

The hypocrisy is total. The biggest single contributor to global crime is the $300bn drugs market, half of it cannabis. In Britain the cannabis market is worth an estimated £68bn, and is the single greatest cause of social disruption and distress. It is a generator of organised crime, urban gangs, anarchic prisons, corrupt policing, teenage suicide and family breakdown.

This is evil enough. Britain’s attitude to medicinal cannabis is unreasoned and cruel. Any research involving it must be licensed, not by the health department but by the Home Office, which still regards cannabis much as the early Victorians regarded chloroform – as a dangerous offence against God’s will. Licences cost £5,000 and researchers must be police-checked. Only a tiny group of cannabinoid products, such as Sativex, can be prescribed for multiple sclerosis “at the doctor’s own risk”. If Britons go abroad to buy such products, they bring them back on pain of imprisonment.

Imperial College London’s leader in this field, David Nutt, sees Britain sliding to the bottom of the research table – even on cannabis derivatives that it invented, such as THCV. Nutt is dismayed as Americans, Germans and Israelis are racing ahead, “knowing that this research is the stuff of future medicine”. Since all other remedies for dementia have proved disappointing, to stand in the way of any apparent breakthrough seems absurd.

This is medieval Britain, where policy is dominated by fear politics and fake news. When in 2000 the Police Foundation committee (on which I served) advised cannabis be downgraded, Tony Blair and Alastair Campbell reacted like scalded cats over what the Daily Mail might say, and killed it. In the event, it was rather supportive.

Since then, all reports on reforming the 1971 Act have been ignored. In 2014 a coalition government study of global drug laws found “no obvious relationship” between criminal sanction and consumption; yet Theresa May as home secretary fought its publication and demanded it be censored.

A year ago, polls showed British opinion had moved in the same direction as America, with almost half in favour of legalisation and three-quarters in favour of medicinal cannabis. Legalisation is a cause that now embraces both liberal left and libertarian right. It is supported by MPs of all parties, by the British Medical Journal and by a cast list of senior scientists and doctors. It also embraces the police, told to implement a law that has lost public consent. One force after another is following Durham’s practice, ignoring cannabis possession in favour of struggling to fight the crime that illegality causes.

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I have never used cannabis, but see it as a medicine that brings relief from suffering to many, and degrees of pleasure to more. It is not a harmless drug. Like alcohol, it can be abused. But the abuse is personal, not to others. It is criminalisation that hurts others.

The British state, at vast human and financial cost, has failed completely to stamp out drug abuse. Drug deaths last year were at an all-time high. A responsible state would regulate such products and help make them safe.

May’s fanatical aversion to drug reform typifies the “nasty” side of her state, an authoritarian nation, illiberal and ruled by alien hobgoblins and prejudices. In the past decade the 1971 Act has criminalised almost a million young Britons, ruining their chances in life. It has crammed prisons with drug-related offences, more than ever before, and slashed the community treatment that is the norm across Europe.

For what? So populist politicians can posture against reason and common sense? At the forthcoming election, Britain’s Liberal Democrats have at last come out for legalising cannabis, after failing to do so when sharing power in coalition. As for Labour and the Conservatives, forget it. Britain’s most desperately needed – and money-saving – social reform is stuck in the dark ages.