London (CNN) -- British Prime Minister David Cameron told lawmakers Thursday that police in London waited too long to begin arresting rioters after unrest broke out Saturday.
"What became increasingly clear earlier this week was that there were simply far too few police deployed onto the streets," he said. "And the tactics they were using weren't working."
This week's apparently orchestrated looting -- which occurred in different places at the same time -- presented "a new and unique challenge," but police changed their approach and dealt with it successfully, he told an emergency session of Parliament.
The violence broke out after a protest over the death of a London man, Mark Duggan, who Cameron said was shot by police.
The Aug. 4 shooting occurred when officers from a police unit that deals with gun crime in the black community stopped a cab carrying the 29-year-old father of four in the working-class, predominantly Afro-Caribbean district of Tottenham, the Independent Police Complaints Commission (IPCC) said.
Cameron promised a thorough inquiry into Duggan's death, but said it did not justify the ensuing violence.
What started as a peaceful demonstration Saturday in front of the police department by community members and Duggan's relatives and friends 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."
The massive police presence that was instituted Tuesday seemed to have had its desired effect in Britain with authorities reporting no major outbreaks of violence on Thursday morning.
Police in Britain are being given more tools to tackle disorder, Cameron told lawmakers, with "every contingency" being looked at, including greater powers to ask suspected troublemakers to remove their masks. Curfew powers will also be reviewed.
More than 1,200 people have been arrested nationwide, Cameron told lawmakers -- who were recalled from their summer break to attend the session -- and if convicted they can expect to go to jail.
In London, police reported 1,009 riot-related arrests, with 464 people charged. Police in West Midlands reported 330 arrests since Monday evening and Greater Manchester Police listed 145.
"Keeping people safe is the first duty of government," Cameron said. "The whole country has been shocked by the most appalling scenes of people looting, violence, vandalizing and thieving.
"It is criminality pure and simple. And there is absolutely no excuse for it."
Cameron said Londoners would see 16,000 police officers -- far more than usual -- on their streets through the weekend, and said "good progress" had been made in restoring order nationwide.
But much damage has been done, with retailers losing more than £100 million ($161 million) over four nights of looting and violence, an analysis found.
Cameron promised government help for families and businesses whose properties have been damaged. They will receive tax breaks and grants, including a new £20 million ($32 million) fund to help affected retailers get back in business, he said.
Street gangs are behind much of the trouble on Britain's streets, he added, saying evidence suggested they had coordinated their looting and attacks on police. Cameron said the government was looking into whether it could act to stop troublemakers from using social media to carry out such crimes.
He urged action -- including social reforms and tough criminal justice -- to deal with groups composed mostly of boys leading a "blighted life" in deprived areas. Britain will turn to the United States for help in tackling gangs, Cameron said, referring to anti-gang efforts in Boston, Los Angeles and New York.
Cameron also said that the "broken society" that led to some children "growing up not knowing the difference between right and wrong" had to change, with parents taking on more responsibility.
But, he added, the troublemakers did not represent the vast majority of young Britons.
The nation now needs 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.
Courts in London and elsewhere have been holding late-night sessions to process those who have been arrested; some people have been jailed.
An analysis conducted by the Centre for Retail Research on behalf of price comparison website Kelkoo reported that retailers have lost £80 million ($129.4 million) in sales.
They lost another £17.4 million ($28.1 million) in looted stock, and face £43.5 million ($70.3 million) in repairs, the analysis said. The total loss could reach £520 million ($840 million) over the coming 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. "But the situation is very fluid, so this figure is likely to change," a spokeswoman told CNN.
In Tottenham, the focus had shifted Thursday to clean-up. Groups handed out brooms to residents, and hundreds took to the streets to sweep up broken glass and other debris.
Police said residents could help them by identifying photographs of looting suspects. The Metropolitan Police and other police forces posted surveillance photos online.
Detectives investigating Wednesday morning's hit-and-run incident in Birmingham in which three young men were killed arrested on Thursday three more males on suspicion of murder. They are ages 16, 17 and 26. A 32-year-old man who had been arrested Wednesday has been released on bail.
The victims, ages 31, 30 and 20, were leaving prayers at 1 a.m. and returning to a gas station they had been guarding to protect it from possible looters when the incident occurred, witnesses said.
And in Ealing, west of London, detectives opened a murder investigation when a man who had been attacked Monday died Thursday.
Police have issued closed-circuit video footage showing a looter suspected of carrying out the assault and appealed to the public to identify him.
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.
CNN's Laura Smith-Spark, Carol Jordan, Ed Payne, David Wilkinson, Anna Stewart and Bharati Naik contributed to this report.