An estimated 30,000 people have braved heavy rain to attend a festival celebrating cannabis. The event started with around 10,000 anti-prohibition campaigners marching from Kennington, south London, to nearby Brockwell Park in Brixton where the Cannabis Freedom Festival was held. Police in the area will next month give only a formal warning to people found with a small amount of the drug. Organisers of the festival said there were no arrests during the day and that policing had been "very low-key", in keeping with the radical scheme due to be introduced on July 2. A spokesman for the International Cannabis Coalition said: "Given the atrocious weather, we were really encouraged by the turnout. It reflects the wide support for ending cannabis prohibition in this country." From next month, police in Brixton - one of the country's foremost illegal drugs markets - will issue an on-the-spot warning and confiscate the drugs but the matter will go no further. They say it will enable them to target their resources on the fight against harder drugs such as crack cocaine. If successful the scheme could be extended to the entire Metropolitan Police area. Police chiefs believe the new approach could take 10 minutes of a constable's time instead of up to 10 hours if the person is arrested, taken to a police station and formally cautioned. The country's most senior police officer, Met Commissioner Sir John Stevens, has backed the plan, describing it as "an innovative step." He said: "We are not turning a blind eye to crime but we have to prioritise."