Cannabis demo: 25,000 due

Up to 25,000 cannabis smokers will take to the parks of London tomorrow in what organisers are billing as one of Britain's largest acts of mass civil disobedience.

The crowd will meet as part of the fifth annual International Cannabis March and Festival.

Drug-smoking Londoners will come out in force, along with crowds in 250 other cities worldwide, to protest against prohibitions on the possession, supply and use of the drug.

Cannabis is being reclassified as a Class C drug in Britain, which means casual users are unlikely to be arrested for possessing or using it. But it is still an offence to have or supply it, and the marchers will demand full legalisation of the drug.

The rally starts in Kennington Park from where there will be an hour-long march to Brockwell Park, Brixton, where music and speeches have been organised.

There will be stalls giving information on the drug, grow tents offering "horticultural and gardening tips" and a kids' play area for parents to leave children during the seven-hour sit in.

"We are doing this with the full co-operation of Lambeth police and the local council," said march organiser Jerry Ham. "But what we will see on Saturday, and what we have done in previous years, is actually the biggest single act of civil disobedience in this country."

"We respect that these people are making a point from their perspective," said a Scotland Yard spokesman. "But there will be a police presence at the march and, while we would not want to provoke a riot or a major altercation, we will intervene if we believe there is reason to do so or if there is a flagrant breach of the law."

The Met says it will stamp down on dealers who use the march to sell cannabis but in previous festivals there have been no arrests for possession or use of the drug.

Lambeth is a borough where police have spearheaded a liberal policy towards soft drugs, and was where controversial police commander Brian Paddick was in charge of a policing policy where officers turned a blind eye to the street cannabis trade to free up resources for tackling hard drugs.