I figure it has to do with all of the social welfare programs that were cut in the UK after the bank bail outs...something that may happen in America soon. I have always said that the only way to get people to rise up would be to stop their welfare checks. Also, the incident involving a questionable police shooting seemed to enrage quite a few; though i personally think they are being a bit ridiculous. The fact remaint that, as in the rest of the industrialized world, average citizens are pissed off at their respective governments. They just want a reason to revolt.
I would also like to mention that I think it's obvious now that the UK's gun laws, which are incredibly strict, have done next to nothing to protect the populace...given the recent rampages. I just wanted to throw in my own political opinion regarding gun legislation. Again, people are mad and many are unemployed. If you have nothing better to do and you're angry at authority, why not start a riot? It worked in Egypt.