A report by the Centre for Social Justice says the arrests of more than 200 leaders of London street gangs in the wake of last year's riots has led to an increase in chaos, violence and anarchy in the capital.
It says the removal of 'elders' from the streets backfired because it created a power vacuum in which younger and more hot-headed members seized control of gangs.
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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.