Speaking on the BBC's Today programme, the controversial chief constable acknowledged that his was a minority view, but he said attitudes were changing.

"I'm certainly out of step with the majority of senior police officers, but not all of them," he said.

"But in terms of society, public attitudes change quite rapidly and you need look no further than drinking and driving: in the space of my lifetime drinking and driving has gone from being socially acceptable, almost the norm, to being socially unacceptable.

"I think that the legalisation and subsequent regulation of proscribed drugs is now inevitable, and I think it's ten years away, not ten months away."

He went on: "It has already happened in for instance Portugal, a full member of the European Union, decriminalised under the existing international treaties.

"The same sort of thing is being talked about across the world."

He said levels of drug misuse across the country might be falling because of better treatment programmes, but the problem was still acute.

'Prohibition doesn't work'

"We're still causing something like £20bn worth of damage to our society every year," he said.

"More than half of all recorded crime is caused by people feeding a drugs habit.

"The government wants evidence-based policy; the evidence is very clear that prohibition doesn't work, it can't work, an enforcement-led strategy is making things worse, not better."

Mr Brunstrom was invited onto Radio 4 by three members of Dyfed-Powys Police, who were guest editing the New Year's Day's edition of the programme.

He also said there was a lot of "scaremongering" and "rumour-mongering" about drugs.

Battle

"Ecstasy is a remarkably safe substance - it's far safer than aspirin," he said.

"If you look at the government's own research into deaths you'll find that ecstasy, by comparison to many other substances - legal and illegal - it is comparably a safe substance."

A spokesman for DrugScope, the UK's leading independent centre of expertise on drugs, said they believe the legalisation of drugs within the next decade is "unlikely".

"Neither the current government nor the leaders of the other parties show any inclination towards drug law reform in the near future," he said.

"And in fact this government has already suggested its desire and its looking closely at reclassifying cannabis from class C to B."

In October, Mr Brunstrom said drugs laws were out of date and that the police are engaged in a battle which they cannot win.

He said he is now campaigning for drugs to be legalised, and for the class A, B and C system to be scrapped.

The police chief's suggestions were criticised by some politicians.