We need to consider not only whether, but also how, to legalise cannabis

The law on cannabis in the United Kingdom is changing, so the debate needs to move on from the simplicities of “decriminalisation now” to a more rounded assessment of harms and benefits.

Sajid Javid, the new home secretary, has announced a review of the medicinal properties of cannabis that seems certain to lead to greater use of the drug for treatment, especially of epilepsy. The case of 12-year-old Billy Caldwell, and the determined campaign of his mother, Charlotte, has, as she said, “bust the political process wide open”.

Despite Mr Javid’s insistence that “this step is in no way a first step to the legalisation of cannabis for recreational use”, common sense – and experience from elsewhere – suggests otherwise. After all, the present situation is unsatisfactory, with cannabis being illegal, but the police making little to no effort to enforce the law on individual consumers. The only argument for this existing arrangement is that the law performs a symbolic function, serving to express society’s disapproval and to discourage use.

The Independent has been nuanced on this subject over the years, given the shifting base of scientific knowledge about the effects of cannabis, and changes in the strength of the drugs reaching the market. However we hope we have been consistent in erring in the side of tolerance and liberalisation. When The Independent on Sunday was a separate publication, it campaigned for the decriminalisation of cannabis as the dawn of New Labour broke in 1997.

Ten years later, it changed its mind, as indeed the drug itself changed. It was influenced by the association between serious mental illness and heavy cannabis use among a minority, mostly young men, increasingly smoking the stronger and increasingly prevalent varieties known as skunk. The argument then was that changing the law would lead to more cannabis use and therefore more psychological harm. That is still a possibility, although the evidence of causation is inconclusive.

We must accept that decriminalising cannabis would almost certainly mean more people will use it. That will have some negative effects, not least in making more people more boring. But alcohol makes people boring too, and if people smoke cannabis instead the overall harm is likely to be lower. What's more, if decriminalisation were to take place, it would need to be accompanied by public information campaigns which emphasised that the move was not akin to encouraging use, or to affirming that cannabis is harmless. And, given the recent successes in public health awareness about cigarettes, do we really want a population that is switching to vaping to acquire a taste for cannabis?

There are other possible benefits of decriminalising cannabis – or, more sensibly, legalising it, so that it can be regulated and taxed. As well as reducing demand for alcohol it may, according to limited American experience, suppress demand for opioids, which, as the US has found, are far more damaging than either cannabis or alcohol.

Regulation and taxation offer the prospect of three important gains: greater safety; cutting the role of organised crime; and raising revenue.

Assessing the purity of cannabis is not as important as with other drugs, such as ecstasy – and the spread of free ecstasy testing at music festivals is a positive step. Nevertheless, it would be necessary to assess the level of the active ingredient in cannabis, THC, not least for the purposes of setting the level of tax. American states have found that crude taxes levied by weight have driven the production of higher and higher THC content cannabis – which not only gets round the tax system, but can lead to smokers taking higher doses than they intended.

Also important to get right before any broader moves are made is the question of how best to bring cannabis to the market. In other words, how will shops be licensed or regulated; what checks will they be required to make of their customers; what health warnings will need to be given? Matters such as this are not side issues: the how is as vital as the decision to proceed or not to proceed.

Indeed, none of the benefits of legalisation are unalloyed. Legalising low-end cannabis would not do much to drive organised crime out of the drugs business. Setting the tax rate high, as in Washington state, can leave most cannabis in the hands of street dealers; setting it too low means passing up the chance to raise revenue that could be used for education and treatment.

Mr Javid’s announcement today recognises, however, that the debate has changed. Medical cannabis was the gateway in the US to the legalisation of the drug for recreational use. Public opinion in the UK has shifted, as it has in the US. People are ready for the gradual recognition, based on evidence – and increasingly on evidence from the US – that the balance of harm versus benefits is shifting.

It is time to move beyond the simplicities of absolutism on either side. Criminalisation of cannabis in all circumstances in unsustainable. Legalisation is not without its problems. Mr Javid has done the easy bit, of reviewing medical use: now he must start on the hard part, of getting the overall balance of the law right and working out what legalisation would look like in practice.