The first details of how London would cope with a terrorist atrocity on the scale of the September 11 attacks can be revealed today.
They include setting up prefabricated mortuaries and using Tubes, trains and buses for a mass evacuation of the capital.
The plan contains details of how to evacuate Heathrow, the Square Mile and Canary Wharf, and how roadblocks would be placed around the M25 to direct people fleeing the city by car.
The Mayor would launch a disaster appeal fund within hours to raise money for emergency care and to assist the bereaved. The Strategic Emergency Plan was drawn up by London Resilience, the body which co-ordinates the emergency services, government departments, transport and utility companies and local authorities.
It is described as a "blueprint for the effective handling of any disruptive incident in the capital", from extreme weather to a sickness-pandemic or a terrorist attack. It has been published online after almost four years of secret planning by officials and politicians. But key details such as evacuation sites or roads to be used as escape routes remain secret due to their sensitivity.
A government source said: "These plans have been worked on since 9/11. Things existed before 9/11 - what was different was the scale and nature of the threat.
"We are not trying to alarm people or scare people. We are trying to reassure them that these plans
exist, and that if something happens there are mechanisms for dealing with a wide range of circumstances."
The 45-page plan sets up a chain of command in the event of a major incident, which it warns could come suddenly - such as a terror attack - or like a "rising tide", akin to the spread of disease.
The Prime Minister would lead the Government's response, with the police in charge of the immediate response on the ground.
The Mayor would act as the "voice of London", making TV appeals and issuing instructions to the public. Media officials would share information via pagers and text messages.
Temporary mortuaries would be set up if fatalities exceeded 75. One came into operation in west London when huge numbers of Britons were feared dead in the Asian tsunami.
Transport hubs have already been identified from which nonstop buses will collect people. Central London train stations would be used and London-bound trains halted.
The plan states that mass evacuation "will always be the last resort", with preservation of life the overriding principle.
It adds: "Mass evacuation will use public and private transport. The Underground, bus and rail networks will be utilised."
There are also plans on what do with huge volumes of rubble from destroyed buildings.
Richard Barnes, chairman of the London Assembly's Safer London committee, said he was reassured after an investigation found "a clear command structure that officers from fire, ambulance and police had been trained in".