London: Unveiling vigorous measures to tackle Britain's worst riots in decades, Premier David Cameron on Thursday promised extra powers to police to quell the violence as a massive clampdown in London and other major cities netted over 1,200 trouble-makers and prevented further chaos.

Police raided houses to hunt down masked youths responsible for four days of violent unrest as calm descended on London and other affected areas in northeastern and southeastern England. Heavy torrential rains also came to the aid of the authorities, making foot movement on the streets difficult.

Cameron, who deployed thousands of police personnel on streets in the affected areas, vowed to act "decisively" to restore order.

Outlining a number of measures to combat the mayhem that overtook his nation shocking the world, he promised new powers to police and law enforcement agencies and state support to those who had suffered losses in the violence.

As a first major step to counter street violence, Cameron announced that police and security agencies had been given special powers not to allow people to move around with masks.

His remarks came as television cameras showed that most of the arson, looting and violence had been carried out by youngsters wearing masks.

"We will not allow a violent few beat us," Cameron said addressing a rare recall of Parliament to tackle the extraordinary situation.

His hard-hitting riposte to violence came as police all over London and outlying counties conducted massive raids on houses arresting over 1,200 people who had been caught on CCTV cameras indulging in mindless violence.

Cameron, who refused to bow down to pressure, did not announce any softening of austerity plans and expenditure cuts, which left-leaning parties and lawmakers have blamed for the malaise that has rocked the nation, whose social and perhaps racial tensions exploded in four nights of bewildering violence.

The Prime Minister said the violence had nothing to do with politics or protests, but it was purely motivated by theft. He vowed that the "climate of fear" will not be allowed to exist on streets.

Cameron as well as his Chancellor of Exchequer George Osborne exuded confidence that nothing would be allowed to impede the country from hosting next year's Olympics, as British Association of Insurance estimated the losses in four days of rioting to excess of 200 million pounds.

Deputy Assistant Commissioner of Police Stephen Kavanagh said the raids to round up suspects had begun overnight and authorities had issued more than 100 arrest warrants.

"More warrants and arrests are not ruled out," he said disclosing that police had photo evidence of the youths and gangs involved in violence.

"We expect hundreds of more people to be in custody by tonight," the high ranking police official said.

Not ruling out the possibilities of involvement of gangs in the violence, Cameron promised to look to the US for help for fighting the street gangs.

"We will look to cities like Boston for inspiration to tackle gangs," the Prime Minister said as he blamed them for helping spark Britain's worst ever riots.

After a relatively quiet night on London's streets, life started to limp back to normalcy as owners of shops and cafes in districts of the capital, where rioters had looted and set fire to shops, put up a brave face and opened for business.

After two days of being shut, London's Oxford street, a shopping magnet for tourists worldwide, stayed open late. In the affluent Indian and Asian-dominated West London district of Ealing, shopkeepers also started to reopen premises.

The copycat riots had spread to cities of Manchester, Salford, Liverpool, Wolverhampton, Nottingham, Leicester and Birmingham from London, where they erupted following the death of 29-year-old Mark Duggan in police firing on Thursday.

Social media may be intercepted

Meanwhile, Britain is likely to assume powers to intercept messages through social media such as Blackberry Messenger, Facebook and Twitter during times of crisis so that such messages are disrupted.

Setting out measures to prevent the kind of disturbances London and other cities witnessed, Prime Minister David Cameron told the House of Commons that people were struck by the ways in which coordinated rioting was organised.

Much of the recent violence in London and other cities had been coordinated through social media, according to police.

"Free flow of information can be used for good. But it can also be used for ill. And when people are using social media for violence we need to stop them," Cameron said.

"So we are working with the Police, the intelligence services and industry to look at whether it would be right to stop people communicating via these websites and services when we know they are plotting violence, disorder and criminality," he added.

When wise counsel won over passion

Emotions ran high during the candlelight vigil in Birmingham in memory of the three young British Asians who were mowed down by a speeding car, but appeals for calm and peace from local residents won over passions for revenge.

Birmingham has a history of uneasy relations between Asians and the Afro-Caribbean community. The last major tension between the two communities was witnessed in 2005 in the Lozells area, where Asians have economically prospered over the years.

Sachdev Virdi, the Indian-origin president of the Asian Rationalists Society of Britain said from Birmingham, "The community has to behave wisely. The police have taken a civilised approach. The effort is to do our best to ensure that the community is not divided".

Candles marked the spot last night where Haroon Jahan, 21, and brothers Shazad Ali, 30 and Abdul Musavir, 31, had been killed late on Tuesday night, allegedly by members of the Afro-Caribbean community.

Both Prime Minister David Cameron and leader of the opposition Ed Miliband on Thursday paid tributes to Tariq Jahan, whose son Haroon was killed. Miliband called Jahan "the true face of Britain".

The Asian identity is often stressed as members of the community are tied together by economic, cultural and social relations. This is reflected in the all-round praise won by Sangat TV, a local community channel devoted to Sikh issues and events, for its coverage of the riots.

Its presenter Upinder Randhawa was close to tears on air while filming a group of distraught Muslim men who had learned about the death of their friend.

At the vigil, there were no politicians, no official community spokespeople or religious leaders, but local men, struggling to know how to manage their grief and anger, The Guardian reported from Birmingham. After prayers and a silent vigil, men took turns to express their views.

Riots to cost nearly 400 mn pounds

The riots across England could cost the British economy a whopping 392 million pounds, new figures revealed. Figures from online comparison site Kelkoo said if the riots in cities outside London continue till Saturday, the bill would surely hit the estimated mark, the Daily Express reported.

Retail stores have already missed out on sales of 80 million pounds as they were forced to close early to avoid trouble. Customers also stayed away from many shopping areas.

Looted stores face a bill of more than 141 million pounds to cover stolen stock and clean-up costs. Tourism is also likely to suffer. Britain could lose 520 million pounds if just one percent of visitors change their plans.

Another likely bill was 200 million pounds for the public who can claim compensation for riot damage.