AL-QAEDA terrorists had to abandon a plan to fly hijacked airliners into Canary Wharf, the London skyscraper, and Heathrow airport after being “rumbled” by British and European intelligence services.

The plot was made public this year but senior Whitehall sources gave further details yesterday of the intelligence work involved.

Reports on ITV News and in a newspaper implied that the attacks had been thwarted recently. But, the sources said, the intelligence operation was in fact completed at least two years ago.

Plots against Canary Wharf, in London Docklands, and Heathrow were confirmed in July when intelligence officers in Pakistan found incriminating files on computers that belonged to one of al-Qaeda’s members.

Mohammed Naeem Noor Khan, 25, a suspected terrorist arrested after a raid in Lahore, Pakistan, was at the centre of al-Qaeda’s computer communications hub. He encrypted and distributed messages between the network’s leadership and agents around the world.

Among the files on Khan’s computers were a plan of the layout of Heathrow and information from reconnaissance of the Canary Wharf complex, including vehicle height restrictions for the underground car parks there.

There were also suggestions for “picture postcard” targets, such as the Houses of Parliament and Windsor Castle, and discussions of potential assassination targets. But the plots referred mainly to planning that pre-dated the attacks in New York and Washington on September 11, 2001.

Whitehall sources said that a huge intelligence operation was also mounted after Sept-ember 11 when it was feared that al-Qaeda would try a similar hijacking over Britain. The sources said that there was credible intelligence that al-Qaeda planners were preparing to send a hijacking team to the UK.

To foil the terrorists, checks were carried out at airports and flying schools in Britain and also in countries in Central and Eastern Europe, from where it was believed that al-Qaeda members might set off.

Further checks on flying schools have been carried out in the past six months as part of continuing anti-terrorist operations.

“They were rumbled,” a source said. “We believe that al-Qaeda recognised that aviation security in the UK was too tight for a repeat of the September 11 attacks in this country and that it was too difficult to hijack an aircraft in our airspace.

“Our firm belief is that the Heathrow and Canary Wharf plot is no longer extant. There is absolutely no evidence of any recent plotting against either of these targets. All the intelligence we had dates back at least two years.”

Some of the key people who were involved in planning the Heathrow and Canary Wharf plots were also by now either “deceased or arrested”. The arrests had taken place outside Britain.

Anti-terrorist agencies also said that there was no intelligence of any current suicide hijacking plot against targets in Britain. Scotland Yard sources were “bemused” by suggestions of a current plot.

Downing Street and the Home Office, stinging from reports that ministers are trying to create a climate of fear before next year’s election, distanced themselves from the story.

A police source said: “If there was information that Canary Wharf was to be attacked, then I think that we would know. There is no credence to reports of any current threat.”

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