The Misuse of Drugs Act has failed utterly and there is no political consensus about the idea of trying anything new

It is 40 years since Parliament passed the Misuse of Drugs Act, establishing the framework that, with periodic tweaks, is used for controlling substance abuse today. Actual drug use has been going on a lot longer, so it is hardly surprising that one legal instrument has failed to kill the habit.

It is remarkable, however, how utterly the system has failed. Drugs are available to anyone who really wants them. The classification system of substances into degrees of harmfulness – A for the worst, C for the least bad – is ignored by users and dismissed by many scientists. Its only practical use seems to be in determining prison sentences and filling our jails with drug users has had no deterrent effect on use.

Meanwhile, the volume of new products coming to the market is growing at an alarming rate. Laboratories in the far east churn out synthetic variants of natural narcotics or make minor molecular adjustments to old drugs, turning them, from a legal point of view, into new ones. According to a report by the UK Drug Policy Commission, revealed in today's Observer, 40 new substances appeared on the streets last year.

These "legal highs" are ignored by the law until their use attracts sufficient media attention. Then they are classified, proscribed and sold, in a more toxic form, on the black market instead of over the counter. In the 40 years since this process began, patterns of actual drug use have been driven as much by fashion as policy. Heroin in the 80s, ecstasy in the 90s, cocaine today. Cannabis is a staple; levels of use vary a bit, but not in correlation to its pointless, politicised journey between classes B and C.

It is hard to think of a legal approach to any other problem that has failed so thoroughly without political consensus emerging around the idea of trying something else. The 40-year regime introduced by the Misuse of Drugs Act has been characterised by a nonstop boom in the misuse of drugs. Surely it is time to rip it up and start again.