A zero-tolerance policy on cannabis is being introduced in Brixton, less than two years after the south London borough pioneered a scheme to relax the law.
The U-turn will add to the pressure for the Home Secretary, Charles Clarke, to abandon the current "softly softly" approach and increase the penalties for having the drug.
The decision by the Metropolitan Police to start arresting anyone caught with cannabis is an admission that the current system of warning people, rather than arresting them, is not working in some inner-city areas.
The police are introducing the tough policy, called "no deal", on cannabis in Brixton following complaints that an increasing number of dealers are openly selling the drug and are harassing passers-by. More cannabis users are also being attracted to the area.
Police will begin a three-month "positive arrest" policy for anyone caught with cannabis in Brixton and surrounding areas from 12 December. At the end the trial, the policy will be reviewed.
Chief Superintendent Martin Bridger, the commander of Lambeth, which includes Brixton, said: "We want people to enjoy coming to Brixton without having to face drug dealing, its associated crime and the intimidating behaviour it can lead to."
Paul McGlone, who represents the Brixton ward of Ferndale on Lambeth council, said: "You only have to walk down Brixton High Street and you face a barrage of offers for you to buy hashish or whatever from aggressive drug dealers."
Rachel Heywood, who chairs the Brixton Area Forum, said she hoped the move would stop "drug tourists" visiting the area.
The move is a remarkable change in approach for the police in Brixton. Four years ago, Lambeth's borough commander, Brian Paddick, sparked a national debate when he ordered his officers to stop arresting people for the possession of small amounts of cannabis and concentrate on dealers of hard drugs. Police found they could save hundreds of hours of time by just warning people with small amount of cannabis rather than arresting them for an offence that might result in a small fine.
The approach was adopted nationally in January 2004 when David Blunkett, as Home Secretary, downgraded the drug from class B to class C. Under the changes to the law, the police ceased to treat possession of cannabis as an arrestable offence in most situations. But they retained the power to designate "arrest zones" where cannabis use was problematic - which is what is happening in Brixton.
Lord Stevens, the former commissioner of the Metropolitan Police, said the changes caused "a massive amount of muddle" and many people believed cannabis had been legalised.