An independent report on the riots that swept England in August has strongly criticised the police response to the unrest.
The Riots, Communities and Victims Panel says the main reason was the perception that rioters would not be challenged by the police.
The panel found there was no single cause of the riots but said it was shocked at the "collective pessimism" among the young people it spoke to.
Riots broke out in Tottenham, north London, on 6 August, two days after the fatal shooting by police of Mark Duggan, 29. Unrest spread to other cities, including Manchester, Birmingham and Bristol.
The panel warned that such riots would happen again unless action was taken.
It said research suggested that between 13,000 - 15,000 people were actively involved in the riots.
It looked at the causes of the riots, how communities responded and ways to avoid a recurrence.
Panel chairman Darra Singh noted it is 30 years since the publication of the Scarman report into rioting in Brixton, south London, in 1981.
''The panel is clear that the riots in August were very different disturbances to those in 1981,'' he said.
''However, it is a sad fact that in some respects, the underlying challenges are strikingly similar.''