UK riots led to the highest ever British usage figures for Twitter

"Although people were glued to the news sites for updates on the unrest, it was Twitter which has benefited the most from traffic as a result of the unrest in London. The real-time sharing of information through Twitter has made the platform the ideal discussion platform to spread updates on major news events like the riots, and yesterday (8 August) was Twitter’s biggest ever spike in UK traffic online.
Twitter accounted for 1 in every 170 UK Internet visits yesterday; by our estimations there were over 3.4 million visits to the Twitter homepage from the UK population alone. To put that in context, Twitter received 15% more visits yesterday than it did around the super-injunctions scandal, the previous biggest spike in its UK history.
Somewhat unusually, the spike in traffic to Twitter was not repeated on other social media websites, especially Facebook. Looking at our postcode data helps to explain why this might be. Twitter is used widely across the UK but the most prolific Twitter users are located in London postcodes."

Source:  Data from Hitwise, reported on their blog, 9th august 2011