The project, set up four years ago, allows 1,000 selected addicts to obtain a daily dose over the counter at one of three special clinics.

Heroin use has not fallen in last four years

Supporters of the experiment now want the scheme to be opened up to unlimited numbers of addicts.

There are an estimated 40,000 hard drug users among Switzerland which has a population of seven million.

Health professionals say most users taking part are gradually being weaned off heroin and many successfully reintegrate into society.

The project also ensures addicts are injecting with sterile equipment and reduces the hazards related to dirty needles such as Aids.

We shouldn't be pushing drugs, say right wingers

Supporters argue that the $30-a-day expense must be offset against the costs of jailing addicts for thieving or trafficking.

Research shows the majority of users on the project stop stealing to feed their habit and most find work and a place to live.

Critics say scheme locks users into addiction

But right-wing politicians say the state, which is responsible for preventing drug abuse, should not be distributing heroin as well.

They believe the scheme locks abusers into their addiction, rather than encouraging them to give up completely.

Supporters of the scheme believe the number will fall if parliament votes to allow as many addicts as possible to take part in the project.