London: An uneasy calm prevailed over Britain's cities on Thursday after four days of rioting and looting, with security being beefed up and a stern warning from Prime Minister David Cameron that law and order will be restored at any cost.

Cameron has convened a special session of parliament to discuss the worst riots in England in decades even as tensions remained high in the violence-hit areas but no major incidents were reported.

Cameron, who vowed to "fight back" to crush the unrest, is expected to outline further measures to deal with recent disorder.

Preliminary estimate of the extent of loss was nearly 200 million pounds, British media reported. Under the little known 1886 Riot Damages Act insurance companies, individuals and businesses can reclaim their losses from local police authorities.

Police have arrested more than 1,000 people and charged nearly 300 in connection with violence in London and other parts.

Cameron, who cut short his holiday in Tuscany to tackle the biggest challenge confronting his 15-month old coalition government, said contingency plans have been put in place for making available water cannons at short notice. Police has already been authorised to use plastic bullets for the first time against rioters.