 Cameron said that the government, police and intelligence services were looking at whether there should be limits on the use of social media sites such as Twitter and Facebook or services such as BlackBerry Messenger to spread organised disorder, and whether to turn off social networks or stop texting during times of social unrest.The number of arrestees in London rose to 922 and 401 suspects had been charged.The police said they had arrested 330 people over the past four nights.