Police guard a shop after looting broke out in Brixton on August 8, 2011 in London


British Prime Minster David Cameron says the police faced “a new and unique challenge” this week, as looting broke out at the same time in different places across the country.

He said police in London acknowledge they initially delayed too long before taking action to arrest rioters and looters, as he addressed Parliament Thursday. The violence first broke out after a protest over the death of a London man, Mark Duggan, who Cameron said was shot by police.

Cameron promised a thorough inquiry into Duggan’s death in Tottenham but said it could not be used as a justification for later violence.

The peaceful demonstration was “used as an excuse by opportunist thugs in gangs, first in Tottenham itself, then across London and then in other cities,” he said. “It is completely wrong to say there is any justifiable causal link.”

Cameron praised the bravery of individual officers in tackling rioters, but said: “What became increasingly clear earlier this week was that there were simply far too few police were deployed onto the streets. And the tactics they were using weren’t working.”

Police in Britain are being given more tools to tackle disorder, he told lawmakers, including greater powers to ask people suspected of causing trouble to remove face masks. Curfew powers will also be reviewed.

More than 1,200 people have now been arrested across the country, Cameron told lawmakers as he addressed an emergency session of Parliament, and if convicted they can expect to go to jail.

“Keeping people safe is the first duty of government,” he said. “The whole country has been shocked by the most appalling scenes of people looting, violence, vandalising and thieving.

“It is criminality pure and simple. And there is absolutely no excuse for it.”

Cameron said London would see a “surge” of 16,000 police officers — far more than the city’s usual policing levels — on its streets through the weekend.

A massive police presence seemed to have had its desired effect in Britain with authorities reporting no major outbreaks of violence on Thursday morning.

But much of the damage has already been done, with retailers losing more than £100 million ($161 million) in four nights of looting and violence, an analysis found.

Cameron promised government help for families and businesses whose properties have been damaged during unrest in England’s cities this week. They will receive tax breaks and grants, including a new £20 million fund to help affected retailers get back in business, he said.

Cameron said the government was looking at whether it could act to stop troublemakers using social media to coordinate looting.

Street gangs are behind much of the trouble on Britain’s streets, he added, saying evidence suggested they had coordinated attacks on police and looting.

He urged action to deal with groups of mostly young boys, leading a “blighted life” in deprived areas, including social reforms and tough criminal justice. The United Kingdom would turn to the United States for help in tackling gangs, Cameron said, referring to efforts in Boston, Los Angeles and New York.

Cameron also said a “broken society” that had led to some children “growing up not knowing the difference between right and wrong” had to change, with parents taking on proper responsibility.

But, he added, the troublemakers did not represent the vast majority of young Britons. The nation now needed to unite to restore its image in the eyes of other countries, he said.

“A year away from the Olympics, we need to show them the Britain that doesn’t destroy but builds, that doesn’t give up but stands up, that doesn’t look back, but always forwards,” he said.

The rioting that began Saturday in Tottenham spread in the ensuing days to other parts of London and then other English cities.

Early Thursday, 16,000 police blanketed London’s streets for a second consecutive night.

They have been authorized to use whatever means necessary to combat unrest, with plastic bullets permitted and plans in place for water cannon to be available if needed. Water cannon have never before been used in mainland Britain.

Courts in London and elsewhere have been holding late-night sessions to try to process the large numbers of people arrested and charged over the unrest.

An analysis conducted by the Centre for Retail Research on behalf of price comparison website Kelkoo found that retailers have lost £80 million ($129.4 million) in sales.

They also lost £17.4 million ($28.1 million) in looted stock, and face £43.5 million ($70.3 million) in repairs, the analysis said. The total could skyrocket to £520 million ($840 million) over the next year, it said, if tourists decide to take their business elsewhere.

The Association of British Insurers estimates the cost of the damage from rioting and looting at about £100 million so far. “But the situation is very fluid, so this figure is likely to change,” a spokeswoman told CNN.

The disturbances are also having an impact on sporting events in the capital.

A football match between Tottenham and Everton scheduled for Saturday has been postponed, a spokeswoman for the Premier League said Thursday. An international exhibition match between England and Holland, due to be played in London on Wednesday, was also canceled.

By midday Thursday, London’s Metropolitan Police Service had arrested 922 people in connection with the violence and charged 401. Police in West Midlands reported 300 arrests and Greater Manchester Police 145.

Steve Kavanagh, deputy assistant commissioner for the Metropolitan Police, said Thursday officers would be raiding dozens of homes in the coming hours and days as they sought to arrest more than 100 suspects.

In Tottenham, where the violence first kicked off, the focus has shifted to clean-up operations. Groups handed out brooms to residents, and hundreds took to the streets to sweep up broken glass and debris.

Streets were largely closed off to cars and pedestrians, said CNN iReporter Spike Johnson in Tottenham.

“Riot vans were lined up in the side streets, council workers repaired roads and shop fronts, and squads of police hung around en masse,” he said. “Residents milled around in shock at the destruction, some were very vocal about their loss.”

In west London, young Sikhs stood guard outside their temple. North of the city, in Enfield, local residents chased after suspected looters. Riot police faced off not with looters but with local residents whose anger verged on mob violence.

Police said residents could help them by identifying photographs of looting suspects. The Metropolitan Police and other police forces posted surveillance photos online.

In Birmingham, the father of a man who was killed in a hit-and-run incident pleaded for calm. Tarik Jahan’s son was one of three men who were mowed down by a car while protecting local businesses from looters, residents said.

Though police had not announced any link between the rioting and the incident, they said they were treating it as a murder inquiry.

“I lost my son,” Jahan told a crowd of more than 1,000 that had flooded the neighborhood. “Blacks, Asians, whites. We all live in the same community. Why do we have to kill one another? What started these riots, and what’s escalated them? Why are we doing this? I lost my son. Step forward if you want to lose your sons. Otherwise, calm down and go home. Please!”

The men — British Pakistanis — were returning at 1 a.m. Wednesday from prayers to a gas station they were protecting when they were hit by the car.

The violence comes against a backdrop of austerity measures and budget cuts. But Cameron, community leaders and police have repeatedly pointed to a criminal, rather than political, motivation for the looting.

Analysts say a mix of economic and social tensions has been at play in the unrest, with deprivation a key factor. Those seen taking part in rioting and looting have been from diverse ethnic backgrounds and span a wide range of ages, and many are young.

The violence began Saturday after a protest over the August 4 shooting death of Duggan, a father of four.

Officers from Operation Trident — a Metropolitan Police unit that deals with gun crime in the black community — stopped a cab carrying 29-year-old Mark Duggan, a black man, in the working-class, predominantly Afro-Caribbean district of Tottenham during an attempted arrest, the Independent Police Complaints Commission (IPCC) said.

It is investigating his death but has not yet said who fired the shot that killed him.

The man’s family and friends, who blamed police for the death, gathered peacefully Saturday outside the Tottenham police station to protest.

The protest soon devolved into violence as demonstrators — including whites and blacks — tossed petrol bombs, looted stores and burned police cars.

On subsequent nights, the violence spread to other areas of London and England. Police characterized the disorder as “copycat criminal activity” by people intent on looting and destruction.