Bob Ainsworth, who oversaw the issue at the Home Office in Tony Blair's government, said the approach of successive administrations had failed.
Mr Ainsworth is the most senior politician so far to publicly call for all drugs, including heroin and cocaine, to be decriminalised.
He said he realised while he was a minister in the Home Office in charge of drugs policy that the so-called war on drugs could not be won.
The big question, unasked by the BBC, is why Mr Ainsworth didn't do anything about this when he was in a position of power. This smells of politics.
Still, if this puts pressure on Lib Dems to put pressure on the government in favour of decriminalisation, that can only be a good thing.
Prohibition is immoral as well as ineffective. Adults should be free to weigh the risks, and decide for themselves which substances they consume. The government has neither duty nor right to intervene.
UPDATE: DK has an excellent post on the same subject here.