Furthermore, state and federal attorneys-general are considering new controls on Facebook to protect children. The government has also been discussing with ISPs a data retention scheme that would involve internet providers storing detailed records of Australians' internet communications for law enforcement agencies to access. Authoritarian states are monitoring these developments closely, eager to see what kind of precedents will be set by Western officials as they wrestle with these evolving technologies, argued Evgeny Morozov, author of The Net Delusion: The Dark Side of Internet Freedom, in The Wall Street Journal. "They hope for at least partial vindication of their own repressive policies," he wrote. Chinese state media are already blaming the London riots on a lack of controls on the internet in Western countries, which is in stark contrast to China's security apparatus, which includes widespread blocking of websites and deep monitoring of online communications. China even shut down the internet in the Xinjiang region for 10 months in 2009 after riots.

"Media in the US and Britain used to criticise developing countries for curbing freedom of speech. Britain's new attitude will help appease the quarrels between East and West over the future management of the internet," an editorial in China's Global Times read. "As for China, advocates of an unlimited development of the internet should think twice about their original ideas." During the mobile reception shutdown in San Francisco by Bay Area Rapid Transit (BART) on Thursday, commuters at stations from downtown to near the city's main airport were affected. BART officials sought to thwart a planned protest over the recent fatal shooting of a 45-year-old man by transit police. Two days later, the move had civil rights and legal experts questioning the agency's move, and drew a backlash from one transit board member who was taken aback by the decision. "I'm just shocked that they didn't think about the implications of this. We really don't have the right to be this type of censor," said Lynette Sweet, who serves on BART's board of directors. "In my opinion, we've let the actions of a few people affect everybody. And that's not fair."

The hacking group Anonymous promised vengeance against BART over the move and followed through on that promise, defacing its website and purportedly stealing user data. "BART officials are showing themselves to be of a mind with the former president of Egypt, Hosni Mubarak," the Electronic Frontier Foundation said on its website. Echoing that comparison, vigorous weekend discussion on Twitter was labelled with the hashtag "muBARTek." Aaron Caplan, a professor at Loyola Law School in Los Angeles who specialises in free-speech issues, was equally critical, saying BART clearly violated the rights of demonstrators and other passengers. "We can arrest and prosecute people for the crimes they commit," he said. "You are not allowed to shut down people's cellphones and prevent them from speaking because you think they might commit a crime in the future." Similar questions of censorship have arisen in recent days as Britain's government put the idea of curbing social media services on the table in response to several nights of widespread looting and violence in London and other English cities. Police claim that young criminals used Twitter and BlackBerry instant messages to co-ordinate looting sprees in riots.

The Prime Minister said that the government, spy agencies and the communications industry 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 disorder. Tory MP Louise Mensch, one of the British Parliament's more active Twitter users, has backed Mr Cameron's call for social networking services to be shut down temporarily during civil disorder, The Guardian reported. "Common sense. If riot info and fear is spreading by Facebook & Twitter, shut them off for an hour or two, then restore. World won't implode," she wrote. The suggestions have met with outrage - with some critics comparing Mr Cameron to the despots ousted during the Arab Spring. In the San Francisco instance, Ms Sweet said BART board members were told by the agency of its decision during the closed portion of its meeting on Thursday afternoon, less than three hours before the protest was scheduled to start.

"It was almost like an afterthought," she told The Associated Press. "This is a land of free speech and for us to think we can do that shows we've grown well beyond the business of what we're supposed to be doing and that's providing transportation. Not censorship." Mr Morozov wrote that people tended to tolerate drastic censorship proposals because acts of terrorism briefly deprived us of the ability to think straight. But Western governments should avoid such knee-jerk reactions as they served only to highlight the perceived hypocrisy in the West's efforts to bring democracy to other parts of the world. "The domestic challenges posed by the internet demand a measured, cautious response in the West," he wrote. "Leaders in Beijing, Tehran and elsewhere are awaiting our wrong-headed moves, which would allow them to claim an international licence for dealing with their own protests." Queensland University of Technology associate professor Axel Bruns, writing in The Conversation, said he felt like repeatedly smacking his head on his desk when he heard Mr Cameron's proposal.

"It is, to be blunt, just staggeringly dumb ... he wants to shut Twitter and Facebook down, just because someone, somewhere might use them to plan criminal activities? You must be joking," Professor Bruns wrote. "By the same reasoning, why not take out the entire internet and phone network as well? Cracking down on social media at home while promoting it as a tool for democracy abroad simply doesn't make sense." He pointed out that social media was used considerably more to report on the riots, to inform locals about which areas were safe, and to co-ordinate the community-led clean-up than they were to plan criminal activity. "Indeed, the images of looters snapped by bystanders, shared through social media sites, are now themselves used by British police to identify the perpetrators," he wrote, adding that British police were themselves using social media sites to identify offenders. Mr Conroy declined to comment.

- with AP This reporter is on Twitter: @ashermoses