The UK is “plainly losing” the war on drugs - and may even be going backwards, Justice Secretary Kenneth Clarke said today.

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.

"The really key thing is to try to work out how to get fewer young people to start experimenting with drugs.

"One thing that does put them off is that they would get into trouble with the police."

He said he did believe one area of improvement was that "friction" between Whitehall departments over whose responsibility it was had been lessened.

It "has not vanished but is very, very much less than it used to be", he said, praising in particular coordination between his department and the Department of Health.

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.

Mr Clarke admitted that "it was news to me" and had sent him diving into the brief prepared for him by officials.

It advised him to say, he revealed, that drug treatment was moving towards a recovery-based approach and long-term methadone use should not be employed "unless absolutely necessary".

He said: "That I believe to be the policy.

"I was not aware that Nice had not changed its advice.

"Nice is not an agency of my department. I think Andrew Lansley and myself, Nice and the prison service had better touch base afterwards about whether we are or are not moving towards a drug treatment system focused on recovery."