Jack Straw said yesterday that he had no problem with the principle of legalising cannabis for medicinal use.

The Home Secretary said the drug "will become available on prescription" if the nine ongoing research trials underway, revealed last month by The Independent, recommended that cannabis or its derivatives could safely be used as a medicine. "I have no problem whatsoever with this in principle," he said. Mr Straw ruled out fully decriminalising the drug, although he accepted there was a "coherent argument" for legalisation on the grounds that its effects were different from heroin or cocaine and no more serious than tobacco or alcohol.

He said the law as it stood, based on the Misuse of Drugs Act 1971, was "pretty sensible". He argued that legalising cannabis would make consumption rise as prices fell and would attract drugs tourists to Britain.

Writing in the News of the World newspaper, Mr Straw stated: "As the Dutch police warn us, the semi-legal trade in cannabis in the Netherlands has helped make that country a safer place for big-time crooks. If we legalised cannabis, Britain could follow."

His argument was dismissed by the Labour MP Paul Flynn, who said possession of cannabis for personal use was decriminalised in Spain, Italy and Portugal as well as Holland.

Mr Flynn, a long-time campaigner for reform of drugs laws, said: "Britain has the harshest laws in Europe and the worst drug problems. Countries with pragmatic, intelligent laws have fewer problems. The UK's mindless prohibition is doing more harm than the drugs themselves." He called for a "legal, licensed" market to replace the "irresponsible, illegal" one.

Sir John Stevens, the Metropolitan Police Commissioner, fuelled the debate yesterday by saying possession of cannabis was a low priority for police and that they could "work with" legalisation to decriminalise it. Sir John, speaking on a trip to New York, said: "Our job is to enforce the law. If the law says it's illegal then we enforce the laws. If they say it's legal in Parliament, then so be it." Scotland Yard later said the Commissioner opposed legalising cannabis but had been pointing out that Parliament makes the law and the police enforce it.