According to Mathew Ingram at GigaOm:
In the wake of the riots in London, the British government says it’s considering shutting down access to social networks — as well as Research In Motion’s BlackBerry messenger service — and is asking the companies involved to help. Prime Minister David Cameron said not only is his government considering banning individuals from social media if they are suspected of causing disorder, but it has asked Twitter and other providers to take down posts that are contributing to “unrest.”
Like that's a good idea.
Is the same going to happen to email providers? (Actually that wouldn't matter either way as so few under 20s use email for much.) Is the same going to happen to people who might be talking to each other, using such subversive technology as mobile phones?
And then how do you decide when someone's causing disorder? "Let's all meet at Domino's Pizza at 6" with the intent of torching it looks rather similar to "Let's all meet at Domino's Pizza at 6" because some friends are plain hungry.
Legislate in haste; repent (and be made to look silly in the press) at leisure.