The communications blackout after the July 7 bombings left ambulance crews and hospitals unaware of the scale of the attacks.
A breakdown in the London Ambulance radio system meant that crews did not know to which hospitals they should take casualties. Starved of information, Great Ormond Street Children's Hospital sent staff racing out to the nearby Russell Square and Tavistock Square bombsites.
The hospital, which was not involved in emergency planning, set up its own field hospital to help ambulance crews who could not get through to the hospitals on standby.
Judith Ellis, a chief nurse, told an inquiry the London Assembly: "If it [a major incident] is on your doorstep, you want to help. Luckily, the field hospital was set up by our staff who were in the Territorial Army who had just come back from Iraq, so we had people who were very good at field hospital set-ups."
One member of staff spent the day scanning for e-mails with information because the telephone network was down. The e-mails did not come.
Ms Ellis urged the NHS to rethink its communications policy in the case of major events: "In London you are going to have staff wanting to help and they need to be told how to step in."
Dr Gareth Davies, a consultant in emergency medicine at Barts and The London NHS Hospital Trust, said radios were only working 10-15 per cent of the time in the aftermath of the blasts. He said: "We relied on runners and ambulance crews passing on information as they dropped patients off. When the last telephone call you receive says eight bombs have gone off, it sounds like Armageddon."Reuse content