The British government often comes up with poorly thought out policy ideas, but in fairness, these ideas rarely end up as actual laws - the obvious logic flaws are picked up on sooner or later. I suspect it's just a case that they needed give out some policy ideas to keep the journalists happy and this is the first thing they came up with.

Anyway, I can't see how removing access to social media would have had much influence on the riots - seems like SMS messages would be just as effective, for organising a riot. Social media just happens to be a cheaper option.