Shops were looted and buildings set alight as police clashed with youths. The trouble also spread to Birmingham, Liverpool, Manchester and Bristol.

Violence first flared on August 6 after a peaceful protest in Tottenham over the fatal shooting of a man by police.

The prime minister is returning early from holiday to chair a meeting of the government's emergency committee Cobra.

David Cameron, who is on holiday in Italy, was due to board a flight on August 8 ahead of a meeting with Home Secretary Theresa May and Acting Metropolitan Police Commissioner Tim Godwin on August 9.

A government spokesman said the prime minister has been monitoring the situation on "an hourly basis".

At least 225 people have been arrested and 36 charged following the riots across London over the past three days, Scotland Yard said.

It added that an extra 1,700 officers had been deployed across the capital on August 8. Nine police forces from other parts of the country were assisting in providing support, as well as the City of London Police and British Transport Police.

Commander Christine Jones, from the Met, said: "The violence we have seen is simply inexcusable.