Cannabis, hash, dope. It's been called many things, but now it may be known as medicine

To the planters of the American colonies who were ordered in 1622 to grow cannabis for the production of sails and rope, the current debate on decriminalisation of such an adaptable plant would be incomprehensible.

To the planters of the American colonies who were ordered in 1622 to grow cannabis for the production of sails and rope, the current debate on decriminalisation of such an adaptable plant would be incomprehensible.

The Romans recognised the medicinal qualities of Cannabis sativa as long as 1,500 years ago, burning it in bedside braziers to give relief to women during childbirth. But for the past 75 years in Britain, the possession of this versatile shrub has been a criminal offence after fears over its harmful properties led to the passing of the 1925 Dangerous Drugs Act.

Since then the debate over whether the dangers of the drug outweigh the benefits of its healing, social and practical qualities has polarised British society to the extent of causing divisions within the Cabinet itself. The current Home Secretary Jack Straw has been prepared to take his own son to the police to admit handling cannabis while Cabinet Office minister Mo Mowlam admits to having smoked it herself.

The original legislation to outlaw cannabis followed a backlash against marijuana smoking in the United States where leaflets were circulated warning of drug pedlars spreading "a powerful narcotic in which lurks: Murder! Insanity! Death!" But by the Sixties, the smoking of cannabis had become a key part of an emerging youth culture. At rock festivals, the brazen use of dope/blow/reefer/spliff/weed became a common signal of defiance of a law which police officers fought vainly to uphold.

It was the arrest of Mick Jagger in 1967 and his three-month prison sentence for possession of a controlled substance (later commuted to a hefty fine) which was to spark off the debate about decriminalisation which has raged for more than 30 years. Some regarded Jagger - who had been suspected by police of smoking marijuana but prosecuted after being found in possession of four sea sickness pills - as a criminalwho had got what he deserved.

But the then editor of The Times William Rees-Mogg said in a leader that the punishment was a "primitive" impulse to "break a butterfly on a wheel".

Mr Rees-Mogg then published a full page advertisement, signed by 50 prominent people, calling for cannabis decriminalisation. They wrote: "Possession ... should be either permitted or at most considered a misdemeanour punishable by a fine of not more than 10 pounds."

Two years later, the Wootton Report, produced by an advisory body set up by the government, concluded that no one should be imprisoned for possessing cannabis and called for penalties to be reduced. The advice was rejected by the Labour home secretary James Callaghan. In 1971, the Misuse Of Drugs Act consolidated existing law but drew a more marked distinction between possession and supply, increasing the sentence for dealers whilst cutting the punishment for users.

The Thatcher and Major years coincided with a surge in drug use among Britain's youth, driven by the dance music explosion and prompting public and media panic and a political backlash.

Tim Malyon, the author of Big Deal: The Politics of the Illicit Drugs Business, said: "The 'War on Drugs' culture started rearing its head and any discussion of decriminalisation of cannabis became a no-no." But as the criminal justice system struggled to cope with the demand for illegal substances - the numbers prosecuted for cannabis possession rose from 18,213 in 1985 to 68,598 in 1995 - some began to look for alternative solutions.

In 1997, the Independent on Sunday newspaper begun a campaign calling for cannabis to be decriminalised and in November 1998 the House of Lords Science and Technology Committee recommended that doctors be entitled to prescribe it, as the medicinal benefits in easing the pain of sufferers of multiple sclerosis, arthritis and other conditions became more clear. The findings of the Lords committee followed a recommendation by the British Medical Association in 1997 that the law should be changed to allow research on the medical benefits of the drug.

Last December, such research began under the auspices of the Medical Research Council. A similar project is being undertaken by the private company GW Pharmaceuticals.

Tony Blair and his hardline Home Secretary have until now resisted all calls for a softer approach. At Labour's last party conference Mr Blair announced another drugs crackdown saying it was an issue which "all governments have ducked for too long". He said he was "petrified of drugs in respect of my own children". Last month he promised again in the Commons to fight the "drug menace at every level".

Two years ago, the government appointed Keith Hellawell as its anti-drugs co-ordinator. While he has been careful not to call for decriminalisation the "drugs tsar" has come to the conclusion that cannabis should be treated with greater tolerance while resources are concentrated on fighting the growing use of more dangerous drugs like heroin and cocaine.

As Mr Hellawell has struggled to produce the evidence which the Government is seeking to show that its drug policies are working, ministers have become unhappy with his performance and Ms Mowlam has been given a new role in overseeing drug policy. The Cabinet enforcer, however, also takes a more benign view towards cannabis. Though not advocating decriminalisation she is understood to support "sensible reforms". Her mother Tina recently suffered a long-term illness and though she did not use cannabis her family is believed to support the drug's use for medical reasons.

Judges and juries have also become increasingly sympathetic to those using and even growing cannabis for the purposes of pain relief. Last week, Thomas Yates was cleared by a jury in Suffolk after police found 40 cannabis plants in his home in Lowestoft. Mr Yates, who has multiple sclerosis, told the court that cannabis was the only drug that eased his pain without unpleasant side-effects.

Since the national drugs information group Release was set up in 1967, one million people have been prosecuted for cannabis offences. Release's spokesman Mike Goodman said: "The issue around the therapeutic and compassionate use of cannabis has come of age and there is no doubt there will be change in this arena in the near future. The prospects for change in relation to social use may take more time but the dialogue is now becoming more clear and constructive."