Al-Qa'ida were planning to hijack aircraft and crash planes into Heathrow airport and London's Canary Wharf, according to a US security report.
The British landmarks were among a number of targets around the world being considered by terrorist operatives.
In one plot, the terrorists were going to use cameras and their flash attachments to conceal bombs and stun guns as part of an "ingenious" plot.
Using the converted weapons, it is thought it would have been possible to access the cockpit and even bring down the plane.
These weapons were to be used against targets in the east coast of the US, the UK, Italy and Australia, but were thwarted in 2003, according to the report.
In the same year, Prime Minister Tony Blair was criticised for deploying the armed forces to Heathrow.
A separate plan to fly a plane into a skyscraper in east London's Canary Wharf was brought to light in 2004.
Details of the Al-Qa'ida plots were revealed in a report by the US Department of Homeland Security, obtained by the US television channel ABC News.
It said a total of nine hijack plots since September 2001 had been uncovered "demonstrating a continued commitment to attack aviation-related targets".
A Homeland Security official was quoted as saying: "Al-Qa'ida planned to hijack flights departing London's Heathrow Airport and crash them into the airport and a skyscraper in the Canary Wharf financial district of London."
The official went on to describe Al-Qa'ida as adapting "to increased aviation security by shifting planned suicide hijackings from domestic carriers to international flights... to take advantage of perceived less effective security screening at some foreign airports."
The report, believed to have been released earlier this month but only seen by the media yesterday, also described an Al-Qa'ida plot involving a US consulate in Pakistan.
It claimed there were plans to fly "an explosive-laden general aviation aircraft into the US consulate in Karachi, Pakistan".
The threat of attacks is persistent, the report said, adding: "The Department of Homeland Security continues to receive information on terrorist threats to the US aviation industry and to the western aviation industry worldwide.
"But there is no recent information to suggest near-term operational planning for an aviation attack within the United States."Reuse content