Image caption Anna receives methadone once a week

Some analysts suggest that lessons can be learned from Portugal's drug laws. So how are things done differently there?

As she waited calmly with fellow drug users queuing for their weekly treatment in Lisbon's main detox centre, Anna was happy to talk about the addiction that has blighted her for the past 15 years.

The 53-year-old drug user, who preferred not to give her surname, said she was now able to lead a normal life because of Portugal's enlightened approach that favours public health over the criminalisation of drug users.

Anna visits Lisbon's 'Centro das Taipas' each week to receive the heroin substitute methadone.

She explained: "I had a good life, and when I started taking drugs I spoilt my life and now I am drug-free again and I am well. When I feel ok I will stop methadone, if necessary on an in-patient basis."

The change in law that led to this treatment was a response to a growing drug problem in the late 1990s.

'No problem'

Portugal had developed a reputation as a gateway for drug trafficking, with more than three quarters of drugs seized destined for other European countries.

By 1999, it had the highest rate of drug-related Aids cases in the EU and there was a growing perception that the criminalisation of drug use was increasingly part of the problem.

So in 2001, the socialist government changed the law to turn possession of drugs into an "administrative offence", sending those caught with drugs for personal use to a "dissuasion board" rather than face prosecution.

Image caption Paulo (with his back to the camera) was given a warning by the dissuasion board

At one of these hearings was a 32-year-old man who had been caught in possession of hashish.

Paulo showed no regret as he explained his case to a social worker and psychologist, saying: "I don't feel I have a problem with drugs, so I don't feel I need to be here".

As this was his first appearance before the board he was just given a warning. If he is caught again, sanctions will be applied.

But far more drug users are taking up treatment as a result of the change in law, an independent study by Dr Alex Stevens from the University of Kent found.

It said the overall numbers of drug users in treatment expanded in Portugal from 23,654 to 38,532 between 1998 and 2008. While between 2000 and 2008 the number of case of HIV reduced among drug users from 907 to 267.

"This is a highly significant trend which as been attributed primarily to the expansion of harm reduction services," it concluded.

Radical change

The advisor of the management board of the Instituto of Drugs in Portugal, Dr Fatima Trigeiros, said its partners had feared decriminalisation would make people flock to Portugal to take drugs, but that did not happen.

"Before the law changed people with drug consumption would fear to come into the treatment structures because they were afraid they would be taken to court," she said.

We have a government that on paper at last is a dream ticket for actually putting in place substantive reforms Danny Kushlick, Transform

"Also we were not tackling first-time users, those who were experimenting, because the time between being caught and the time they were taken to court was too long. Now they are being taken to the dissuasion boards in 72 hours."

Would the British government ever entertain such a radical change? The Home Office says decriminalisation is not the answer; instead it wants to reduce drug use and drug-related crime and help addicts kick their habit.

But there is evidence the prime minister thought differently when he was in opposition. Eight years ago, David Cameron wrote in the Daily Telegraph, that "politicians need to get up from behind their barricades and look at what works, rather than what sounds good".

He called for a declassification of some drugs so cannabis would move from class B to class C and ecstasy from A to B, even allowing some severe heroin users access to injecting rooms.

As a backbench MP, Mr Cameron called on the government to raise a debate at the United Nations on legalisation and regulation. It was the clearest indication ever given by a future British prime minister of a desire to rethink drugs policy.

The charitable think tank "Transform", which is lobbying for a change in the law, is hoping the prime minister's past views will prevail.

Its head of external affairs, Danny Kushlick said: "We have a government that on paper at last is a dream ticket for actually putting in place substantive reforms that are going to shift resources from criminal justice and towards public health."

With difficult public sector cuts looming, drug reform may not be the first priority of the British government, but it is now consulting on the UK Drugs Strategy.

Reformers say if they want to reduce spending on drugs they could do worse than to look to Portugal.