Politicians, youth leaders and those affected by violence have been meeting at a conference in London aimed at tackling gang culture.
As Liz Wickham found, it's thought the arrest of more than 200 gang leaders in the wake of the 2011 riots may have created a power vacuum, in which younger gang members have grabbed power, on a wave of violence:
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In a wide-ranging Peston on Sunday interview, he said Parliament security needs reviewing and the PM's counter-terror strategy is flawed.
The terror attack carried out by Khalid Masood at Westminster that left four people dead lasted less than two minutes say police.
Two knives were found at the scene in Islington, North London, and the suspects fled on foot before being arrested.