Why do people in rich countries riot and tear up their own neighborhoods?
In my mind there are two explanations, psychological and political. Psychologically, the riots are an expression of the anger and frustration that dogs human life in every time and place. They are sign that awful emotions boil beneath the surface of placid-seeming human communities and ordinary-looking people. No place is really safe from political extremism, because everyone is full of anger, and clever demagogues have always been able to direct that anger against convenient targets.
Politically, riots represent the breakdown of democracy. The way the modern world works is that people behave themselves and do their jobs in exchange for lives that are materially nice and make some sort of spiritual sense. When things are tough, democratic politics is supposed to provide an outlet for their unhappiness, in the form of crusades to change things, promises of improvement, or at least leaders who feel their pain. Riots show that many people think they are not getting the deal they were promised, and that nobody in authority cares.
Thus the explosion in Britain. Large classes of British people feel that they work hard for no reward, while people with the right Public School connections get cushy lives. And right now Britain has a government that has openly pledged to do nothing to help them, and that has in fact promised more pain and delivered on their promise. The Tory government says Britain cannot afford the generous government it had in the past, and it cannot do anything much about the recession because it has no money, so people will just have to tough it out. They may be right, but that is not a message calculated to soothe poor people worried about their futures. Millions of young Britons feel the pinch of want and see only more misery in the future, and their leaders have been consumed by a scandal about newspaper reporters tapping people's phones. You see the result.
Government austerity sounds good in paneled rooms where everyone has a good job, but on the mean streets it looks like straight up cruelty. If British authorities were as surprised as they say by these riots, they were fools.