In my article in the current issue (subscribe!) about this spring's abortive "Jasmine Protests" in China, I mention how hard the Chinese authorities cracked down on social media, as a way of thwarting protests before they happened and of apprehending would-be organizers. In certain parts of Beijing and other cities, text-message transmission -- a main means of Chinese communication -- was blocked altogether. The "real" versions of Facebook, Twitter, and YouTube are banned, and the Chinese counterparts were heavily interfered-with.
Obviously constraints on Twitter, Facebook, YouTube, and similar social media were hallmarks of autocratic response during the "Arab Spring" protests as well.
Did David Cameron not read a single foreign news story this past year? Did he have no idea what camp he was placing himself in, with his call to block social media as a way of controlling violence in England? ("When people are using social media for violence we need to stop them" etc. "Free flow of information can be used for good, but it can also be used for ill." During the Jasmine era, I read more or less those views, from Chinese officials, about the need to get tough.)
Let's stipulate that violence and looting are different from non-violent protest, and much more deserving of being stopped; that the United Kingdom, despite being more thickly covered with surveillance cameras than China, is overall a vastly freer society; and that unlike the United States, with its First Amendment, the United Kingdom has never had an absolutist commitment to freedom of speech.