British Premier David Cameron has unveiled vigorous measures to tackle the country's worst riots in decades. He promised extra powers to police to quell the violence. Cameron warned rioters that they will be tracked down, charged and punished for what they have done. The police have arrested 1,300 trouble-makers so far and prevented further chaos. Police raided houses to hunt down masked youths blamed for unrest. Meanwhile, calm prevailed in London and other affected areas in northeastern and southeastern England.