Telephone chaos: Londoners found themselves unable to contact friends and family in the aftermath of yesterday's attacks, as government action and widespread panic combined to disrupt the capital's telephone networks.
A surge in calls after the explosions put the communications system under extreme pressure, with BT saying the sheer volume of calls was causing delays.
But some of the downtime was the result of a government emergency plan known as Access Overload Control coming into effect. This allows various parts of the telephone network to be shut down completely or prioritised for use by the emergency services. Parts of London came under these restrictions yesterday.
A spokesman for O2 confirmed that the network had been instructed to implement Access Overload procedures in some of the most severely affected areas. "We've been asked by the police to provide priority access to the emergency services team in and around the Aldgate area," he said.
He also said users were aided by contingency plans which tried to alleviate some of the problems. "We're able to temporarily increase capacity by decreasing the quality of a call, so we can carry more calls at any one time."
It remains unclear whether the shutdown was used to prevent any potential terrorist communications or even the use of mobile phone signals to trigger explosions, as happened in the Madrid bombings of 2003.
A spokesman for mobile network 3 said it had continued to operate services despite the increased demand in central London.
Not all commuters were unable to let their loved ones know what was happening. Julian Ball, who was in Tavistock Square when a bus exploded, said the problems seemed to be intermittent. "Just after the explosion, people were saying that they couldn't make calls," he said. "But there were lots of people around talking on mobiles that were working - the network seemed to start again very quickly."