By Alison Roberts
BBC News, in Lisbon
Tory leader Michael Howard has pledged a future Conservative administration to reverse the government's relaxation of the cannabis laws, to take effect next week, dismissing the reform as "absurd" and confusing.
But in Portugal, where the possession and use of small quantities of any drug - hard or soft - was decriminalised by the then Socialist government in 2001, the centre-right coalition that took power a year later opted to leave the reform in place.
"The government came in thinking in terms of destroying these measures, but once such steps are taken, you don't go back," Socialist Party leader Eduardo Ferro Rodrigues told BBC News Online.
"However great the temptation to turn back, it won't."
Fernando Negrao, the former police chief whom the new government chose to head the IDT, Portugal's Institute for Drugs and Addiction, agrees.
"This government not only kept the reform in place, but reinforced the health aspect of it, by bringing the institute under the Ministry of Health," he said.
"There were fears Portugal might become a drug paradise, but that simply didn't happen."
Under the 2001 law, consuming drugs is still illegal, but anyone caught with up to 10 daily doses - defined for each drug, by weight - for their own use is not arrested and cannot go to jail.
Instead they are taken to a police station, their details noted, and they are ordered to attend a hearing at one of 18 regional "dissuasion commissions".
Users caught with less than 10 daily doses of any drug are not arrested
The commission can send an offender for treatment if he or she is an addict, impose a fine, or let him or her off with a warning.
"Portugal's experiment is unique," said Mr Negrao.
"It decriminalises drug use, but leaves administrative penalties in place."
Some police representatives have complained that dealers can easily get around the new law, by carrying just a few doses at a time.
The national director of Portugal's main urban police force, the Policia de Seguranca Publica, recently called for a lower cut-off point, to tighten the noose on dealers.
Supporters of the law counter that it does not stop someone being charged with dealing, even if they are carrying just one dose, because it is up to police and public prosecutors to decide whether there is sufficient evidence of dealing.
In any case, according to Dr Luís Patrício, director of the Taipas CAT, or rehabilitation centre, in downtown Lisbon, the figure of 10 doses has no medical basis.
And while it might be normal for a consumer of hashish to have more than 10 doses in their possession, it would not be for a heroin user.
One major problem is that courts around the country are not applying the law consistently.
But those who framed it say this just means there is a need for greater coordination between the new dissuasion commissions and the judicial system.
Portugal's - and now the UK's - legislative reforms are part of a European pattern.
In its 2003 report, the EU's drug monitoring agency noted that member states are taking an increasingly pragmatic approach, adapting legislation to facilitate the treatment and rehabilitation of drug users and addicts - even as their security forces are given wider powers to crack down on trafficking.
The EU agency noted a 34% increase in the previous year in the availability of substitution treatment - principally methadone - across the continent.
Some 400,000 addicts now receive such treatment, with the biggest rise in countries with low initial provision, including Portugal.
There has been little systematic evaluation of the results of such measures, though.
In Portugal, a study of the impact of the reform has only just started.
Health and social workers here say that years of official neglect - in which needle-exchange schemes were a rarity - are to blame for Portugal's soaring rate of HIV infection.
Once the lowest in the EU, it is now the highest, after Spain.
The Socialist government also pushed through legislation allowing for so-called shooting galleries - where addicts could inject drugs under the supervision of health professionals.
But it is up to local councils to take the initiative and none has.