I don’t think the London riots of 2011 have one simple explanation. But for one view of why these things happen and the legitimacy of some subsequent reactions, you could not write a better piece than this:
“When powerful men abuse it, the law becomes an offensive weapon for them and a shield against the weak, and the pretext of public security is always the most dangerous scourge of the people. The most necessary and perhaps the most difficult task in government is to show strict integrity in rendering justice to all, and above all to protect the poor against the tyranny of the rich. The worst has already happened when there are poor people to defend and rich people to restrain. The full force of the law is felt only by those in between; laws are equally powerless against the rich man’s wealth and the poor man’s destitution…
One of the most important things for a government to do, therefore, is to prevent extreme inequality in wealth, not by depriving the rich of their possessions, but by denying everyone the means of accumulating them; and not by building poor-houses but by ensuring that the citizens do not become poor.”
The Social Contract, Jean-Jacques Rousseau, 1775.