Home Secretary Jack Straw has conceded that "there is a coherent argument in favour of legalising cannabis" - but remains opposed to the move.
Mr Straw, writing in the News of the World, insisted that the case for legalisation was fatally flawed, and the move would risk making Britain the centre of the European drugs trade.
But he did allow for the possibility that cannabis might be made available on prescription to relieve pain if medical experts ruled it was safe.
Mr Straw argued that legalisation would probably see consumption increase while imposing heavy duties on the drug would only encourage smuggling.
But he accepted that there was not necessarily a direct link between cannabis use and addiction to hard drugs, and said: "Although the Police Foundation did not go the whole way to recommend this, I accept that there is a coherent argument in favour of legalising cannabis."
Earlier this week a report by the Police Foundation charity had recommended that people caught with small amounts of cannabis or Ecstasy should not be sent to prison.
One of Britain's top police officers, Metropolitan Police Commissioner Sir John Stevens, added to the cannabis debate by suggesting he would not be unduly concerned if the drug was legalised.
Sir John, speaking to the Sunday Express during a fact-finding trip to New York, said: "We are, as police officers, all about enforcing the law. That's what we're here to do. In London, with robberies and murders up, cannabis cannot be a priority.
"If cannabis was legalised we'd be fine with it because that's a policeman's job. I'd work with it.
"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."
He added: "I'm not saying legalise it. If policemen start querying laws, we're in trouble."
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