Almost anybody who takes a sustained, unprejudiced look at the current drugs laws eventually reaches the conclusion that they are hopelessly unfit for purpose.

The Misuse of Drugs Act 1971 must be one of the least effective pieces of legislation ever enacted. At that time, there were perhaps 10,000 problematic drug users in the UK; now there are nearly 300,000.

The Downing Street Strategy Unit concluded that "government interventions against the drugs business are a cost of business rather than a substantive threat to the industry's viability".

In April, an academic paper for the UK Drug Policy Commission warned that imprisoning drug offenders for long periods was not cost-effective. In March, a Royal Society of Arts commission - which included a recovering addict, a senior police officer, a drug treatment specialist and a Telegraph journalist - decided that "drugs policy should, like our policy on alcohol and tobacco, seek to regulate use and prevent harm rather than to prohibit use altogether".

The authors would deny it, but the logic of these reports is that cannabis, cocaine, Ecstasy, heroin and the rest should be legalised.

The harm the various drugs do is irrelevant. Their prohibition has failed, just as prohibition of alcohol once failed in America. Calls for politicians to "get tough" are, as the RSA observes, "meretricious, vapid and out of date".

Since 1995, the numbers imprisoned for drug offences have risen by 111 per cent and the average length of their sentences by 29 per cent. A different approach, based on regulation, offers a chance to reduce the harm done by drugs, and at lower cost.

Yet politicians just fiddle with the classifications of substances, moving them up or down the rankings as though they were running a hotel guide. So Gordon Brown has asked the Home Secretary, Jacqui Smith, to look again at the classification of cannabis, which, scientists report, is probably more dangerous than generally thought when it was downgraded three years ago.

The result is another parade of politicians coming forward to confess to youthful cannabis use which, oddly, none of them enjoyed at all.

Cannabis is an example of the nonsenses created by the 1971 act"s simplistic classification system. Stronger types of cannabis are now on sale, we are told, and research shows a link with schizophrenia.

This is like saying Chablis should be banned because cognac is much stronger and because some people become alcoholics, with dire effects on themselves, their families and society.

All drugs, legal and illegal (including gambling and pornography), vary in their effects according to how strong or pure they are, who takes them, and where, when and how they take them. The classification system cannot allow for this and is, in any case, full of anomalies.

Coca leaves are in class A, alongside crack cocaine, even though the drug in its raw state is largely harmless. Ecstasy is also in class A, though it causes 25 deaths a year against 652 for heroin, which is taken far less widely.

Magic mushrooms, another class A drug, do nothing more than make eccentrics more eccentric. If we are trying to send "messages" to young people about the dangers of drugs, as press and politicians claim, we do it in a pretty confusing way. Many who try one class A drug without ill effects may well conclude they can all be taken freely.

The RSA commission proposed scrapping the 1971 act and putting all drugs, including alcohol and tobacco, within a single regulatory framework.

Some drugs in some forms might remain illegal but their illegality would be placed in a coherent continuum, making some drugs available to certain groups in controlled circumstances, as most prescription drugs are, and others more freely available under licence, as alcohol and tobacco are.

But as the Transform Drug Policy Foundation (www.tdpf.org.uk) says, nobody should pretend that legalisation would solve "the drugs problem", however it is conceived. Many - perhaps most - users handle drugs without significant harm to themselves or others.

Where drugs lead to crime, addiction and family breakdown, they are nearly always associated with wider social problems. The best way to wage war on drugs is to step up the war against poverty.