Boosted by its overwhelming victory in the referendum on devolution yesterday, the centre-left Government of Romano Prodi has moved to dismantle yet another legacy of the Berlusconi era by overturning its “zero tolerance” drugs policy.

The change will restore the distinction between “hard” and “soft” drugs, and will increase the amount of cannabis a person can possess without being arrested as a suspected dealer.

During its first month in power the Centre Left, which won local elections last month as well as the general election in April, has reversed the policies of Silvio Berlusconi’s five-year administration on issues from Iraq to significant infrastructure projects.

Livia Turco, the Minister of Health and a member of the former Communist Democrats of the Left, said today that she would act immediately on the amount of cannabis permitted, an administrative measure that does not require parliamentary approval.

She said the amount of cannabis allowed for personal use — 500mg — would be doubled. Nearly 10 per cent of Italians smoke cannabis regularly, according to a recent survey. A third of Italian teenagers between the ages of 15 and 19 say they have smoked it at least once.

Paolo Ferrero, the Welfare Minister, who is a Communist, said he would ask Parliament to repeal the “zero tolerance” policy and re-establish the distinction between hard and soft drugs. The emphasis would be on “prevention rather than punishment” and “treatment and rehabilitation rather than repression”. This would help to fight illegal drug-dealing by the Mafia, Signor Ferrero said.

However, Antonio Maria Costa, executive director of the UN Office on Drugs and Crime, issued a warning this week that cannabis posed “health risks” similar to those caused by heroin.

In the 2006 World Drug Report, he said cannabis had become more potent in recent decades and Governments that maintained “inadequate” policies “get the drug problem they deserve . . . Policy reversals leave young people confused as to just how dangerous cannabis is”.

Daniela Santanche, a member of the Far Right Alleanza Nazionale — the moving force behind “zero tolerance” — said Signora Turco’s decision would “send a terrible message to young people that drug use is OK”.

The new drugs policy has also raised alarm among Catholic members of the centre-left coalition. The Vatican objected strongly this month when Signor Ferrero suggested that Italy might introduce supervised “shooting galleries” where heroin addicts could inject themselves in a controlled, hygienic environment.

A number of nations, including Switzerland, Germany, Spain, Australia and Canada, have supervised “drug-consumption centres”. But the International Narcotics Control Board says this appears to condone hard drugs and thus undermines the UN’s prohibitionist policies.

Signor Ferrero also caused a furore recently by declaring that “many professional people in Italy, including politicians” use cocaine.

Health experts say there has been an 80 per cent rise in cocaine use in Italy over the past ten years. There are also an estimated 300,000 heroin addicts.