The instant messaging service on BlackBerry smartphones, thought to be used by London rioters to organise themselves, may be shut down at the request of the police tonight, as Benjamin Cohen reports.

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Tottenham MP David Lammy is among those calling for the BlackBerry Messenger system (BBM for short) to be shut down tonight, in an attempt to prevent protesters using it to organise themselves.

Channel 4 News understands that there have been no requests from the Home Office to suspend the BBM service and that it would be unlikely to be something that Research in Motion (RIM), the maker of BlackBerry, would agree to in any case.

However, RIM told Channel 4 News that the company is currently assisting the police with requests for BBM information and data.

While social media outlets such as Twitter are, for the most part, searchable and accessible to the police, BBM is a closed system where users have to mutually agree to contact each other.

It's incredibly popular with teenagers because BBMs can be sent for free to anyone with a BlackBerry from anywhere in the world. BlackBerries are considerably cheaper than rival smartphones from Apple, or those running the Google Android system.

These two points mean that a lot of the teenagers taking part in the riots are BlackBerry users. An Ofcom report last week confirmed that BlackBerries are the most popular mobile devices among 16-24-year-olds.

Channel 4 News also understands that there have been no requests from the Home Office to suspend the BBM service and that it would in any case be unlikely to be something that RIM would agree to.

It is pretty clear that teenagers are using the "personal message" feature to add effective status updates - shared with all of their contacts - on which streets, shops or buildings to attack. This is rather like a Twitter update, except it is only seen by the people you wish to see it.

Similarly, users can create groups of their friends to send messages to, perhaps announcing a change in location, or to discuss what to do next. However, unlike Twitter, these conversations are completely private and therefore not available to the police.

The Regulatory Investigative Powers Act (RIPA) gives the police powers to request information from mobile phone companies and from the owners of BlackBerry - Research in Motion (RIM) - in order to detect and prevent crime. We understand that the police are accessing these messages.

There is some speculation that police may request RIM to switch off the BBM service during this evening, essentially creating some sort of curfew. However, sources pointed out to me that this could lead the rioters to switch to other forms of closed messages such as Facebook or the mobile app WhatsApp.

As it stands, should the police wish, they can in theory access the messages currently being sent using BBM. This may be harder with systems such as WhatsApp, a Silicon Valley-based company with no base in the UK, which means it may be harder to request information from it under RIPA legislation.

In a statement, Patrick Spence, managing director of global sales and regional marketing for RIM, said: "We feel for those impacted by this weekend's riots in London. We have engaged with the authorities to assist in any way we can.

"As in all markets around the world where BlackBerry is available, we cooperate with local telecommunications operators, law enforcement and regulatory officials. Similar to other technology providers in the UK, we comply with The Regulation of Investigatory Powers Act and co-operate fully with the Home Office and UK police forces."