LONDON (AP) — Britons swept up, patched up and feared further violence Tuesday, demanding police do more to protect them after three nights of rioting left looted stores, torched cars and blackened buildings across London and several 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, 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. Police in Britain generally avoid tear gas, water cannons or other strong-arm riot measures. Many shops targeted by looters had goods that youths would want anyway — sneakers, bikes, electronics, leather goods — while other buildings were torched apparently just for the fun of seeing something burn.

Police said plastic bullets were “one of the tactics” being considered to stop the looting. The bullets were common in Northern Ireland durings its years of unrest but have never before been used in mainland Britain.

But police acknowledged they could not guarantee there would be no more violence. Stores, offices and nursery schools in several parts of London closed early amid fears of fresh rioting Tuesday night.

“We have lots of information to suggest that there may be similar disturbances tonight,” Commander Simon Foy told the BBC. “That’s exactly the reason why the Met (police force) has chosen to now actually really ‘up the game’ and put a significant number of officers on the streets.”

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.

“The public wanted to see tough action. They wanted to see it sooner and there is a degree of frustration,” said Andrew Silke, head of criminology at the University of East London.

London’s beleaguered police force called the violence the worst in memory, noting they received more than 20,000 emergency calls on Monday — four times the normal number. Scotland Yard has called in reinforcements from around the country and asked all volunteer special constables to report for duty.

Police launched a murder inquiry after a man found with a gunshot wound during riots in the south London suburb of Croydon died of his injuries Tuesday. Police said 44 officers and 14 members of the public were hurt, including a man in his 60s with life-threatening injuries.

So far over 560 people have been arrested in London and over 100 charged, and the capital’s prison cells were overflowing. Several dozen more were arrested in other cities.

Prime Minister David Cameron — who cut short a holiday in Italy to deal with the crisis — recalled Parliament from its summer recess for an emergency debate on the riots and looting that have spread from the deprived London neighborhood of Tottenham to districts across the capital, and the cities of Birmingham, Liverpool and Bristol.

Cameron described the scenes of burning buildings and smashed windows as “sickening,” but refrained from tougher measures such as calling in the military to help police restore order.

“People should be in no doubt that we will do everything necessary to restore order to Britain’s streets and to make them safe for the law-abiding,” Cameron told reporters after a crisis meeting at his Downing Street office.

Parliament will return to duty on Thursday, as the political fallout from the rampage takes hold. The crisis is a major test for Cameron’s Conservative-led coalition government.

A soccer match scheduled for Wednesday between England and the Netherlands at London’s Wembley stadium was canceled to free up police officers for riot duty.

A wave of violence and looting raged across London on Monday night, as authorities struggled to contain the country’s worst unrest since race riots set the capital ablaze in the 1980s. Groups of young people rampaged for a third straight night, setting buildings, vehicles and garbage dumps alight, looting stores and pelting police officers with bottles and fireworks.

Rioters, able to move quickly and regroup to avoid the police, were left virtually unchallenged in several neighborhoods, plundering stores at will.

Silke said until police were seen arresting large numbers of rioters, it will be hard to control the rioting.

“People are seeing images of lines of police literally running away from rioters,” he said. “For young people that is incredibly empowering. They are breaking the rules, they are getting away with it, no one is able to stop them.”