Cannabis has its dangers, and there is room for argument about how to minimise the harm. But heavy-handed reliance on the criminal law is a failing approach that has been tried for long enough

It is impossible to know how many people have been deterred from using cannabis out of deference to the law. Decades of prohibition have not prevented the drug from establishing itself as a part of the repertoire of psychoactive substances that British people use for leisure and, for a few, non-recreational medication. Despite the theoretical threat of prosecution, cannabis use has become sufficiently uncontroversial for stories about David Cameron dabbling in his youth to have surfaced without measurable impact on his standing as prime minister.

That is not to say the drug is harmless. It appears to put young users at a heightened risk of developing serious mental illness, although only a small minority will be afflicted. Heavy, long-term use is associated with a number of unhappy social and physical conditions, although cause and effect are always hard to disentangle. And, of course, smoking is a dangerous habit with or without cannabis thrown in. The challenge for policymakers is to draft laws that deal with some citizens’ proven appetite for drugs while maximising safety for all, in accordance with the best available evidence. British governments have routinely failed that test. So the publication this week of a report by an expert panel, outlining a potential model of cannabis decriminalisation, is welcome as a step towards rational debate. The report, commissioned by the Liberal Democrats ahead of their spring conference this weekend, envisages a regulated system of legal sale and small-scale production, with a pricing mechanism that steers users towards milder forms of the drug.

Such a document is always vulnerable to criticism from all sides. For libertarians, it looks like another futile effort by the state to manage pent-up market forces. For prohibitionists it is another slip down the slope towards unbridled, licentious mass intoxication. The whole exercise is academic in any case, since the current government has no interest in such a scheme. Its recent effort at legislation in this area, the psychoactive substances bill, created an unenforceable blanket ban on pretty much any chemical compound that might be ingested for kicks. This demonstrated lazy, wilful ignorance of the practical realities of drug use and how best to police it. The Home Office is interested in neither scientific evidence nor lessons from overseas in this field.

There is no perfect template for reform. Different countries have had vastly different experiences. Culture, fashion, demographics and economics all play a part – arguably a bigger part – than state enforcement. But the international trend is moving away from the crudest form of ban-and-punish regime. Most cannabis users do little harm to themselves or others, except by funding organised crime, a function of illegality. Many who might otherwise dabble unscathed end up harmed by the consequences of prohibition: street products of unpredictable strength; career-ending convictions for minor offences; retail contact with gangsters.

Decriminalisation would not fix all the problems with cannabis, and – even if that path were pursued – it is not guaranteed that the model advocated this week would be the best variant. But it is obvious that the existing regime is failing and that a rational, evidence-led review is overdue. Anything that steers the debate a little in that direction must count as progress.