Most in riots had criminal records: London mayor

London: Three-quarters of those arrested in Britain's riots last month had criminal records, London's mayor said on Tuesday, blaming the UK's criminal justice system for failing to turn offenders away from crime.

"What was going to make you more likely to riot? It was previous contact with the police, and that's the problem that we need to tackle," Mayor Boris Johnson told the House of Commons Home Affairs Committee.

The four days of rioting, triggered by a fatal police shooting August 4 in north London's Tottenham neighbourhood, were the worst civil disturbances to hit Britain since the 1980s.

Five people were killed and scores of stores were looted and buildings burned in several cities, including London and Birmingham.

The Ministry of Justice says more than 1,500 people have been arrested and have appeared in court to answer charges from the riots.

Some 22 per cent of them were aged 10 to 17, and 91 per cent were male.

Johnson said three in four had a criminal record, but a full 83 per cent of those arrested have had previous contact with police.

Johnson's comments echoed those of Justice Secretary Kenneth Clarke, who said in an article in the Guardian newspaper that Britain's justice system was failing to deal with a "feral underclass, cut off from the mainstream in everything but its materialism."

"In my view, the riots can be seen in part as an outburst of outrageous behaviour by the criminal classes, individuals and families familiar with the justice system, who haven't been changed by their past punishments," Clarke wrote.

Tim Godwin, the acting head of the Metropolitan police, said police initially focused on known offenders including gang members.

As more suspects are arrested, he said the proportion of those with criminal records may decrease.

He added it was "absolutely essential" analyse the type of previous offences committed by rioters. "We have in London been seeking to speed up justice, make it more relevant, make it more relevant to communities, and that's something that we need to do," Godwin said.

"The amount of people who have previous convictions does pose questions for us."