LONDON: Thousands of extra police officers flooded into London on Wednesday in a bid to end Britain's worst rioting in a generation. An eerie calm prevailed in the capital, but unrest spread across England on a fourth night of violence driven by diverse and brazen crowds of young people.Scenes of ransacked stores, torched cars and blackened buildings frightened and outraged Britons just a year before their country is to host next summer's Olympic Games, bringing demands for a tougher response from law enforcement. Police across the country have made more than 1,100 arrests since the violence broke out over the weekend.In London, where armored vehicles and convoys of police vans patrolled the streets, authorities said there would be 16,000 officers on duty, almost triple the number present Monday. They said a large presence would remain in the city through the next 24 hours at least.The show of force seems to have worked."Without wishing to speak too soon it's been reasonably quiet for us so far tonight," London's Fire Brigade said in a message posted to Twitter earlier in the evening. "Let's hope it stays that way."But outside the capital, chaos was spreading.In the northwestern city of Manchester, hundreds of youths, some looking as young as 10, rampaged through the city center, hurling bottles and stones at police and vandalizing stores. A women's clothing store on the city's main shopping street was set ablaze, along with a disused library in nearby Salford.Manchester's assistant chief constable Garry Shewan said looting and arson had taken place there on an unprecedented scale."We want to make it absolutely clear, they have nothing to protest against," he said. "There is nothing in a sense of injustice and there has been no spark that has led to this."Britain's riots began Saturday when an initially peaceful protest over a police shooting in London's Tottenham neighborhood turned violent. That clash has morphed into a general lawlessness in London and several other cities that police have struggled to halt.While the rioters have run off with sneakers, bikes, electronics and leather goods, they also have torched stores apparently just for the fun of seeing something burn. They were left virtually unchallenged in several neighborhoods, and when police did arrive they often were able to flee quickly and regroup.With police struggling to control the violence, some residents stood guard to protect their neighborhoods. Outside a Sikh temple in Southall, west London, residents stood guard and vowed to defend their place of worship if mobs of young rioters appeared. Another group marched through Enfield, in north London, aiming to deter looters.In a potentially troublesome development, one far-right group said that about 1,000 of its members around the country were taking to the streets to deter rioters."We're going to stop the riots _ police obviously can't handle it," Stephen Lennon, leader of the far-right English Defense League, told The Associated Press. He warned that he couldn't guarantee there wouldn't be violent clashes with rioting youths.Anders Behring Breivik, who has confessed to the bombing and massacre that killed 77 people in Norway last month, has cited the EDL as an inspiration.Meanwhile virtually every major city in England was seeing some form of unrest.In the central England city of Nottingham, police said rioters hurled firebombs though the window of a police station, and set fire to a school and a vehicle outside a second police station, but there were no reports of injuries. A total of 90 people were arrested in attacks on stores, a college, a community center and cars.Some 250 people were arrested after two days of violence in Birmingham, where police have launched a murder investigation after two men were killed and another critically injured in a traffic collision. It wasn't immediately clear if the deaths were linked to the rioting. Police are also looking into unconfirmed reports of shots fired in a restive inner-city neighborhood.In the northern city of Liverpool, about 200 youths hurled missiles at police and firefighters in a second night of unrest, and the area's police force reported 44 arrests.There also were minor clashes for the first time in the central and western England locations of Leicester, Wolverhampton, West Bromwich, Bristol, and the western city of Gloucester, where police and firefighters tackled a blaze and disturbance in the city's Brunswick district.In London, stores, offices and nursery schools had closed early Tuesday evening amid fears of fresh rioting. Several usually busy streets were quiet as cafes, restaurants and pubs also decided to shut down for the night.Many shops had their metal blinds pulled down, while other business owners rushed to secure plywood over their windows before nightfall.In east London's Bethnal Green district, convenience store owner Adnan Butt, 28, said the situation was still tense."People are all at home, they're scared," he said.Senior officers said they were considering the possible use of plastic bullets, blunt-nosed projectiles designed to deal punishing blows to rioters without penetrating the skin. Such weapons, formally called baton rounds, still are used to quell riots in Northern Ireland but have never been used by police on Britain's mainland.UK Prime Minister David Cameron's government rejected calls by Conservative lawmaker Patrick Mercer and some members of the public for strong-arm riot measures that British police generally avoid, such as tear gas and water cannons."They should have the tools available and they should use them if the commander on the ground thinks it's necessary," Mercer said.The disorder has caused heartache for Londoners whose businesses and homes were torched or ransacked, 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 the criminology department at the University of East London.So far 768 people have been arrested in London and 167 charged, including an 11-year-old boy, and the capital's prison cells were overflowing. Britain's Crown Prosecution Service said it had teams of lawyers working 24 hours a day to help police decide whether to charge suspects, allowing them to quickly clear police station cells.A total of 111 officers and 14 members of the public have been hurt so far in the rioting, including a man in his 60s who was attacked as he attempted to put out a fire started by members of a mob.Police said the injured man had been tackling a blaze in a garbage bin, when he was set upon by several rioters. "It was quite a grave assault and his condition is causing us some concern," said police commander Simon Foy.The unrest has been Britain's worst since race riots set London ablaze in the 1980s.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. Britain's soccer authorities said they were in talks with police to see whether this weekend's season-opening matches of the Premier League could still go ahead in London.Prime Minister David Cameron cut short a holiday in Italy to deal with the crisis, reversing an earlier decision to remain on his vacation. He recalled Parliament from its summer recess for an emergency debate on the riots Thursday.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 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.Other politicians visited riot sites on Tuesday, but for many residents it was too little, too late.Deputy Prime Minister Nick Clegg was booed by crowds who shouted "Go home!" in Birmingham, while London Mayor Boris Johnson, who flew back overnight from his summer vacation, was heckled on a shattered shopping street in Clapham, south London.Johnson said the riots would not stop London from "welcoming the world to our city" for the Olympics."We have time in the next 12 months to rebuild, to repair the damage that has been done," he said. "I'm not saying it will be done overnight, but this is what we are going to do."The violence had its genesis in the fatal police shooting of Mark Duggan, a 29-year-old father of four who was gunned down in Tottenham on Thursday under disputed circumstances.Police said Duggan was shot dead when officers from Operation Trident, the unit that investigates gun crime in the black community, stopped a cab he was riding in. A protest demanding justice on Saturday devolved into a riot, which spread to neighboring parts of London on Sunday and by Monday had spread across the capital.Duggan's death resonated in part because it stirred memories of the 1980s, when many black Londoners felt they were disproportionately stopped and searched by police. Their frustration erupted in violent riots in 1985.But the rioters who've taken to the streets since Sunday have been extremely diverse, those in central England appeared to be mostly white and working class.The Independent Police Complaints Commission, which is investigating Duggan's shooting, said a "non-police firearm" was recovered at the scene, but that there was no evidence it had been fired, or that Duggan had fired a weapon at police. An inquest into Duggan's death was opened Tuesday, but a full hearing will likely take several months.Seeking explanations for the unrest, some pointed to rising social tensions in Britain as the government slashes 80 billion pounds ($130 billion) from public spending by 2015 to reduce the country's huge budget deficit, swollen after the country spent billions bailing out its foundering banks.But many rioters appeared simply to relish the opportunity for unchecked violence Monday night. "Come join the fun!" shouted one youth as looters hit the east London suburb of Hackney.