The system crash was a result of a Denial of Service (DoS) attack where hackers bombard the target with repeated communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. Such attacks usually lead to a server overload.
A report titled ‘Issues with Email’ from the police revealed that the attack had a major impact on the performance and availability of its computer system which took several days to return to normal and had subsequent unintended consequences. The report states “During early August 2011, the WMP email system experienced a substantial failure, the details of which are currently the subject of an ongoing criminal investigation.”
This revelation comes after a recent report into the causes of the riots involving hundreds of interviews with those involved revealed that anger with police was one of the major causes of the riots, with people saying they felt the riots were anti-police riots. Other causes included lack of money, jobs or opportunity and the increase in student tuition fees. http://www.guardian.co.uk/uk/2011/dec/05/anger-police-fuelled-riots-study
In Birmingham according to eyewitnesses the riots started after police shut down the city centre and harassed black youths and kettled large groups of people. During the riots a police station in Handsworth was set on fire. https://www.indymedia.org.uk/en/regions/birmingham/2011/08/483457.html