In unprecedented scenes of rioting, violence on Tuesday raged across London and spread to three other cities, as police fought rioters to contain Britain’s most serious unrest, raising questions over security of the 2012 Olympics.

Rioting and looting has spread across London, with unrest flaring up in the central city of Birmingham, the western city of Bristol and the northwestern city of Liverpool.

The third cricket Test between India and England is scheduled to be held at Edgbaston, Birmingham, from 10^th August.

On the third night of riots in London, gangs of masked youth on Monday night looted shops, attacked police officers and set fire to vehicles and garbage dumps in raging violence, sparked by the killing of a youth in police shooting in Tottenham, reminding many of racial unrest in the 1980s.

Clashes in Hackney – one of the five boroughs in which the 2012 Olympics will be held – between police and groups of youths were shown live through helicopter cameras, besides at least one car set on fire on the third night of violence.

Over 200 people have been arrested till Monday night as the police continued to grapple with trouble spreading to newer areas.

Much investment has been made in recent years in Hackney in view of the 2012 Olympics.

Prime Minister David Cameron is returning early from holiday to discuss the unrest, which appeared to be led by youths alienated by years of underemployment which left them feeling marginalized even before the economic downturn.

Scotland Yard has deployed an extra 1,700 officers to deal with the unrest in the capital.

Violence started on Saturday in Tottenham district when a peaceful protest over the police shooting of Mark Duggan, a 29-year-old local man, turned violent.

Trouble has since spread to areas of London, such as Islington, Enfield, Walthamstow, Oxford Circus and now Hackney.