By Gordon Corera
Security Correspondent, BBC News
An official US report has confirmed al-Qaeda planned to hijack flights from Heathrow and fly planes into the airport and a Canary Wharf skyscraper.
Canary Wharf is said to have been one of the targets
Reports of such a plot had surfaced in the media before but have not previously been confirmed.
It is believed the plot was disrupted by security services, although arrests are not thought to have been made.
The report lists nine attempts by al-Qaeda - aside from 11 September - to attack aviation targets worldwide.
Crashed into targets
One of these is the plot to fly into Canary Wharf. Another is an attempt in the summer of 2003 to use camera flash attachments as stun guns as well as cameras to disguise bomb components.
In this plot, the airliners were to be crashed into targets in the east coast of the US, Australia, Britain and Italy.
But Australian Attorney-General Philip Ruddock has said the report is based on a flawed US intelligence assessment from three years ago, which was later corrected.
Other plots are well known, including that of the so-called shoe-bomber Richard Reid and attempts to use portable surface-to-air missiles to attack planes, including one in Kenya.
The original reports of a possible plot against Canary Wharf emerged in late 2004, but the details were murky and officials declined to confirm them.
In February 2003, military vehicles were deployed to Heathrow Airport to deal with a suspected terrorist threat, a move which proved controversial. It is not believed the deployment was linked to the same Canary Wharf plot confirmed by the US report.
The Department of Homeland Security report, dated 16 June 2006 and marked unclassified, was first reported by ABC News in the US and has since also been seen by the BBC.
It makes clear that al-Qaeda remains interested in attacking aviation targets and "likely desires a successful repeat of a 2001 suicide hijacking against the United States".
It lists a number of ways that it could use aircraft as weapons or target different parts of the industry. Amongst the areas of concern are the use of lasers to blind or distract pilots.
Three hundred and eleven possible laser incidents have occurred since late November 2004 although the number has recently declined.
The attacks were planned in the wake of the 11 September hijackings
Another fear is the transfer of a particular tactic used in Iraq to attack US military helicopters being used against commercial helicopters elsewhere.
Improved security has helped protect aviation, although al-Qaeda also continually appears to be searching for new approaches and probing for vulnerabilities, for instance trying to take advantage of less effective security screening in some countries.
The report says the department "continues to receive information on terrorist threats to the US aviation industry worldwide; however, there is no recent information to suggest near-term operational planning may be under way within the United States".