Britain began flooding London's streets with 16,000 police officers Tuesday, tripling their presence as the nation feared its worst rioting in a generation would stretch into a fourth night. The violence has turned buildings into burnt out carcasses, triggered massive looting and spread to other U.K. cities. Police said they were working full-tilt, but found themselves under attack -- from rioters roaming the streets, from a scared and worried public, and from politicians whose cost-cutting is squeezing police numbers ahead of next year's Olympic Games. London's Metropolitan Police force vowed an unprecedented operation to stop more rioting, flooding the streets Tuesday with 16,000 officers over the next 24 hours, nearly three times Monday's total. Although the riots started Saturday with a protest over a police shooting, they have morphed into a general lawlessness that police have struggled to halt with ordinary tactics. The riots and looting caused heartache for Londoners whose businesses and homes were torched or looted, and a crisis for police and politicians already staggering from a spluttering economy and a scandal over illegal phone hacking by a tabloid newspaper that has dragged in senior politicians and police. London residents wait to be allowed through a police cordon to help council workers with the clear up after the rioting that took place the previous night outside Clapham Junction railway station in Battersea, London, Tuesday, Aug. 9, 2011. Britons swept up, patched up and feared further violence Tuesday, demanding police do more to protect them after three nights of rioting left trails of looted stores, wrecked cars and burned buildings across London and several other cities. An employee of a looted shop cleans up debris in the aftermath of riots in the Clapham area of London Tuesday, Aug. 9, 2011. London mayor Boris Johnson, front center, walks away after addressing local residents waiting to be allowed through a police cordon to help council workers with the clear up at after the rioting that took place the previous night outside Clapham Junction railway station in Battersea, London, Tuesday, Aug. 9, 2011.