Dangerous lines

The most visible technology during last week's terrorist attacks on London was the mobile phone. People were using the devices to let family and friends know they were OK, to check and spread the news, and to take digital photographs of events as they unfolded.

Mobiles were a key part of communications for emergency services - and were widely suspected to have been used by the terrorists, too. They have become key weapons in terrorists' armouries. And this is one of the reasons why, as part of its emergency plans, the Government has the power to shut down mobile networks. The only problem is that, as well as stopping terrorists, this also disrupts the legitimate use of mobile phones.

In the immediate aftermath of the attacks, there was certainly downtime on the mobile networks - many people were unable to contact family and friends. This was mainly due to the surge in calls after the explosions, which put communications systems under enormous strain. But some of the downtime was due to the Government bringing its emergency powers into play under a protocol called "Access Overload Control". These powers allow it to shut down networks totally or prioritise them for emergency services.

A statement from the network operator O ₂ confirmed that the company was instructed to implement the Access Overload procedures: "During the course of the day, the police requested priority access for the emergency services in parts of central London. We granted this request, which was subsequently removed as the congestion eased."

Another measure taken by O ₂ and other operators to deal with the demand was to use a procedure called half-rate coding, which allows more mobile calls to be made using existing bandwidth, but with reduced voice quality and little or no mobile data or video services. Emergency personnel are given priority under this procedure, too.

Experts now say that mobile phones weren't used to actually detonate the London bombs - they were in the Madrid bombings last year - which explains why the Government didn't use its powers to shut down the networks completely. "I doubt cell phones would have been used in the London bombings," says Raymond E Foster, a retired Los Angeles policeman and co-author of the forthcoming book Global Terrorism: From Cold War to Flaming-Hot War. "Because of the problems with signal penetration, using cell-phone technology seems like a bad idea for underground detonation. One of the bombs detonated in a very deep tunnel, which rules out the possibility that it was triggered remotely."

Mobiles could have been used as timers. But if they were used in this way, shutting down the networks wouldn't have made any difference - calls would have been stopped, but not the mobile phones themselves.

While the Government's emergency powers to shut down networks would seem to be in all our best interests, there are those who feel it could work against us. "One of the problems with the Government having the power to close down or limit mobile-phone communications is that it stops ordinary people being able to tell each other what is going on," says Ian Henshall, author of 9.11 Revealed: the Facts Behind the War on Terror. "This could have serious implications when you consider that initial news reports insisted that there was a power surge on the Underground. The real news reports came from everyday citizens calling friends and families and telling them the truth - that terrorists were mounting an attack on the Underground. If the Government shut down mobile-phone communications, then the reality of what was happening wouldn't get out for some considerable time. All you'd get is the official line, which they would justify as preventing panic, but it could lead to greater loss of life."

However, Foster feels that shutting down mobile networks around bomb sites is justified, "but you would have to be pretty sure there was a device and it would take time to implement". He points out that such measures are not taken in the US. "You couldn't easily shut down cell-phone networks in the States, or at least it would be very impractical. There are too many vendors, and you would need a court order to shut the system off. Even if you had the protocol in place to shut down the system without a court order, you would still need to call all the companies."

The fact that the US cannot easily shut down mobile networks as in the UK sets off alarm bells for Henshall. "We should strongly question why the British Government has set up A ccess Overload emergency powers, and ask whether it is truly in the public interest," he says.

In any large-scale emergency, mobile-phone networks can go down due to overload. But according to the wireless industry expert John Green of US-based Business Edge Solutions, the next-generation wireless networks may be better able to handle the heavy traffic that comes during emergency situations.

"As the technology moves on, the ability of a single cell to cope with more simultaneous transactions will increase over time," Green says. "And new technologies will also help considerably."