Social networking and mobile phones have been blamed by some for fuelling last week’s riots in the United Kingdom. But now police say they were able to use the technology to head off attacks at high-profile targets.

While some of the less academically gifted rioters published their intentions on Twitter or Facebook, some ringleaders communicated via the messaging system on BlackBerry devices. That allowed them to send messages to multiple people with plans to attack particular locations, without the details being instantly publicly available. Indeed, manufacturers Research in Motion received an unwelcome publicity coup as “to BBM” became a widely used verb in media coverage.

Now the assistant commissioner of London’s Metropolitan police force says officers were able to use information gathered from both Twitter and BBM posts to discover the locations of several planned attacks, including high-profile shopping districts and the 2012 Olympics complex, and divert police resources to protect the areas. It should be noted there has been little report of major numbers of arrests in these areas, though it’s possible the police presence deterred rioters.

Early reports of the police comments suggested the force had broken into the BBM network and intercepted messages. Closer examination suggests it’s more likely the operation involved reading the message history on devices confiscated from those who were arrested.

Research In Motion is not publicly commenting on exactly what co-operation it is giving to police, though it’s understood it is providing as much assistance as possible. It appears that providing the details of who sent a message, from what location and at what time may be enough to serve as legal evidence, even if the content of the message isn’t available.

The comments add a further dimension to an ongoing debate about government powers to shut down communications. Prime Minister David Cameron said officials would look into ways of preventing those suspected of planning criminal activity from using technology.

There’s some confusion about whether he meant shutting off particular users, or forcing entire sites or services to close in times of emergency. Several politicians from the governing Conservative party have called for the latter, though there have been strong political and practical arguments against such a policy. The acting head of the London police says he considered asking for a temporary block on public access to social media but that “The legality of that is very questionable and additionally, it is also a very useful intelligence asset.”

That debate comes at the same time US lawyers, politicians and civil rights groups are discussing the shutdown of cellphone services in four public transport stations in San Francisco last week when protestors were planning to gather. The most vigorous opposition comes from those who believe the move breached the first amendment. And as should probably have been expected, the website of the Bay Area Rapid Transport operators came under attack from “hackitivist” group Anonymous.