London riots: More than 1,000 arrested as unrest continues
Deputy Assistant Commissioner Stephen Kavanagh said raids to round up suspects began overnight, and more than 100 warrants would be executed.
Hugh Orde, head of the Association of Chief Police Officers, said there would be "hundreds more people in custody" by the end of the day.
Deputy Prime Minister Nick Clegg said the "sociological debate" about the origins of the violence was for the future.
"Right now it's important that people are reassured that their streets are made safe, their homes are made safe and society is allowed to move on," Clegg told BBC radio.
The London police said it would keep up the huge operation — involving 16,000 officers — for at least one more night.
Tensions remained high even in the absence of any major incidents.
There was a brief outbreak of trouble in Eltham, southeast London, where a group of largely white and middle-aged men who claimed to be defending their neighborhood pelted police with rocks and bottles. Police said the incident had been "dealt with" and a group was dispersed.
There were chaotic scenes at courthouses, several of which sat through the night to process scores of alleged looters and vandals, including an 11-year-old boy.
The defendants included Natasha Reid, a 24-year-old university graduate who admitted stealing a TV from a looted electronics store in north London. Her lawyer said she had turned herself in because she could not sleep because of guilt.
Also due to appear in court were several people charged with using social networking sites like Twitter and Facebook to incite violence.
Other cities where looters had rampaged earlier this week also came through the night largely unscathed, though for the first time minor disturbances were reported in Wales.
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