Charles Kennedy: I don't. But why shouldn't they?

The law is completely out of step with public views on cannabis

Since the election we have truly seen politics on the move. Labour has advocated more radical private involvement in public services than even the most ardent Thatcherite would have dared. Michael Portillo has emerged as the "liberal" candidate for the Conservative leadership. To cap it all, Peter Lilley has called for the legalisation of cannabis.

It is all a far cry from nearly two years ago when, in one of my first interviews as the newly elected Liberal Democrat leader, I confirmed my support for long-standing party policy on drugs – namely, that a royal commission should be established to examine all aspects of the issue. This led to loud headlines and an even louder condemnation from one Ann Widdecombe.

The Lilley conversion marks a watershed since then and, with the new Home Secretary calling for an "adult, intelligent debate", we may be on the verge of rationality. But if David Blunkett really wants such a debate, there needs to be an authoritative forum. A standing royal commission or similar is surely the best. Although for the moment the new Secretary of State may say he has ruled this out, there is time for reconsideration – particularly if this issue is still on the agenda of the Conservative Party after their leadership election is over.

Mr Blunkett seems to prefer a bottom-up approach, with the police trying out different tactics where and when they can. That's a useful strategy, but it's only part of the answer. It leaves Parliament outside the debate. It leaves experts out in the cold. And it leaves the country with a sense of drift.

But above all, it leaves those of us who want a debate on drugs with a duty to promote one, and to advance our own proposals. That's one reason why the Liberal Democrats have already started our own far-reaching inquiry, which will take evidence from a wide range of people and organisations, and report for a decision by our party early next year. Inevitably, this will have a substantial focus on cannabis, on which the public appears to have a much more liberal attitude than many politicians.

Millions of people have used the drug – 25 per cent of 16- to 59-year-olds according to the 1998 British Crime Survey – yet the law currently makes those people criminals. That seems not only to be an unenforceable position, but also, quite frankly, an insult to many decent people throughout the land. Is an 18-year-old who smokes a joint at a campus party really in the same category as a dealer in crack cocaine?

I believe the present situation has become untenable. For a start, cannabis should be legalised for medical use. It has proven benefits for sufferers of, for example, multiple sclerosis, and it is callous to deny them relief from their condition. Occasional court rulings have already reflected this compassionate view.

The Police Foundation's Runciman committee proposes moving towards the decriminalisation of cannabis for recreational users, and it is my view that this should happen. So let's be clear about what the Police Foundation's recommendations would and would not mean. It would not mean government pretending that cannabis was harmless, or allowing it to be available freely on street corners. It would not mean that the dangers of cannabis as a "gateway" to harder drugs were overlooked. The courts would still be able to use fines to discourage people from using the drug, to send the signal that it is harmful. And, most importantly, the traffickers, who use cannabis to move people on to harder drugs, would still face prison.

Implementation of the recommendations would, however, mean cannabis became a Class C drug, instead of Class B, so people would no longer find themselves in prison for possessing it for personal use. If prosecution for possession were the exception, we would no longer be criminalising millions of people just for use of cannabis, which stops them visiting countries such as the US and harms their job prospects. This cannot be an appropriate response to such a widespread activity.

But changing the usual consequences of using cannabis is only the start of reassessing drugs policy. As a "problem", cannabis is a sideshow compared to hard drugs. Cocaine is powerfully addictive, leading to serious psychological and medical problems. Heroin is just as bad. And with both drugs, there are the dangers caused by the criminal nature of suppliers: impure drugs which have dreadful consequences, the ability of dealers to up the price once somebody is addicted, and the crimes to which people are driven to feed their habit.

The dangers of hard drugs mean that it is hard to apply the same civil liberties arguments as to cannabis. But we have to recognise that the current system for dealing with hard drugs is not working either. It is too lucrative for too many people, and it is becoming too widespread for many things that the police can do to make a major difference.

That means we have to find better methods of undercutting the criminals. There are many ways of doing this. Perhaps the best option, one that a royal commission could investigate seriously, is to allow doctors broader powers to prescribe drugs or appropriate substitutes to addicts. That might not stop people taking the drugs in the first place, but it may mean that we can more effectively remove them from the cycle of addiction and crime that befalls them. Of course, any such scheme should be aimed at getting people off drugs entirely, but people will have a clear choice. Continue to take drugs from criminals, or visit your GP and join a programme that will allow you to kick the habit.

Under the regulations made in 1985 under the Misuse of Drugs Act 1971, there is already a system which allows the Home Secretary to license doctors to prescribe some of the most dangerous drugs, aside from drug alternatives such as methadone. But there needs to be a clearer understanding of which kinds of treatments work. There is now a growing body of evidence from the UK, the US and elsewhere that could inform a royal commission.

But we won't be able to move forward unless we have the kind of sustained analysis of the evidence that a body a royal commission could provide. The kind of debate that is necessary can never take place as long as the broad issue of drugs is shrouded in fear. Nobody has a monopoly on wisdom. That's why the advice of a royal commission on drugs would be so useful if there is in the near future to be any widely agreed change in the law, and coherent strategies aimed at preventing misuse of drugs. This is the best approach to provide the country with the constructive debate it deserves – a debate in which the public and politicians engage with the experts, and the yah-boo of party politics is relegated to the place it deserves.

Charles Kennedy MP is leader of the Liberal Democrats