Emergency services are assessing how successful they were in response to a mock terrorist attack in London.
'Casualties' were treated in decontamination tents
The exercise, centred at Bank tube station on the London Underground, involved fire, ambulance, police and medical staff.
Initial reactions after the one-day exercise ended on Sunday were optimistic that it was a success.
However, a London Fire Brigade spokeswoman said it was too early to get feedback as there were so many agencies involved.
The Minister for Civil Resilience, Nick Raynsford, said lessons would be learned from the exercise.
"There will always be room for improvement following an exercise of this kind and we will certainly make full use of the lessons learned to enhance London resilience," Mr Raynsford said.
Major findings "where appropriate" could be published, he said, but did not specify a date.
Teenage police cadets acted as passengers in a Tube train that was stopped 50 yards short of the platform after the driver reported a chemical attack.
New equipment worth millions of pounds, including chemical suits, was tested in the exercise.
Five hundred emergency services staff cordoned off the streets, rescued the passengers, decontaminated them and took them to University College Hospital.
The exercise has been criticised in some British newspapers, particularly as the first passengers were not rescued for 30 minutes.
Chief fire officer Ken Knight said an exercise involving the closure of the busy heart of the city would not have been practical.
Assistant chief ambulance officer Philip Selwood said the biggest difference between Sunday's exercise and a real chemical attack would be that the effects of some substances may not be immediately apparent.
"Scores of casualties could begin presenting themselves at hospitals around London at different times following an attack," he said.
BBC security correspondent Frank Gardner said the aim of testing the new equipment and coordination between the emergency services was a success.
But he said the controlled conditions of the rehearsal - which was carefully planned months in advance - could only achieve so much.
"If this were real life they would probably have had thousands of terrified members of the public to deal with and that would be a very different story," he said.
BBC home affairs correspondent Guy Smith says plans are in place to evacuate substantial parts of the capital if an attack is launched.
The plans "are continuing to be drawn up by the Metropolitan police and other emergency services to provide rest and reception areas in the home counties," he said.
But evacuating the capital under current plans are voluntary and are only intended as a last resort, the government has said.
Ken Lodge, managing director of SIP Services which protects VIPs and government personnel around the globe told BBC News the weekend's test seemed to go far enough.
But he said the procedure must now much be broadened to organise the mass evacuation of inner city people.
"The public should be made aware of these evacuation plans and routes, but some information must be kept secure for it all to work under emergency conditions," he said.
Mayor of London Ken Livingstone said the exercise would help save lives in the event of a terror attack.
He said: "We recognise if someone's prepared to give their life in order to kill, it's most probably impossible to stop them getting through.
"Our job is to put into place the things that minimise the loss of life when they do get through."
And Transport Secretary Alistair Darling said: "We want to test the new equipment that's available to the emergency services, we want to make sure London's resilience is as strong as possible," he said.
"It's comparatively small scale, but an essential part of our work."