The UK is "plainly losing" the war on drugs - and may even be going backwards, Justice Secretary Kenneth Clarke has said.
But he insisted he was personally opposed to decriminalisation and that the Government had "no intention whatever" of relaxing the law.
Mr Clarke delivered his gloomy assessment when asked at the home affairs select committee what his long ministerial experience of dealing with the issue had taught him. "I have not reached the stage of that blinding insight about exactly how we are going to improve our record, is the honest truth," he told the cross-party panel.
"We have been engaged in a war against drugs for 30 years. We're plainly losing it. We have not achieved very much progress. The same problems come round and round. But I do not despair - we keep trying every method we can to get on top of what's one of the worst social problems for the country and the biggest single cause of crime."
Pressed on whether decriminalisation could be a solution, he added: "The Government has no intention whatever of changing the criminal law on drugs.
"I have frankly conceded that policy has not been working. We are all disappointed by the fact that far from making progress it could be argued we are going backwards at times. But my own purely personal view is that I would be worried about losing the deterrent effect of criminalisation of youngsters who start experimenting."
Mr Clarke also vowed to investigate after prison chiefs told the committee they had not changed policy on using methadone despite a new Government anti-drugs strategy.
He expressed surprise at evidence given by Richard Bradshaw, director of offender health for the National Offender Management Service (NOMS), that its treatment of heroin addicts using the prescription substitute remained unchanged.
Mr Bradshaw, who gave evidence while Mr Clarke was in the room awaiting his session, was asked by Tory MP Nicola Blackwood if there had been any switch in the line of the new strategy.
"The simple answer is no, because we have Nice-approved guidelines around the treatment of methadone which had have been established since 2006 so the integrated drug treatment system - which combines clinical with psycho-social - is the same as we have been applying since 2006," he told her.