Soon after the September 11, 2001 attacks in the United States, Osama bin Laden instructed his Al Qaeda network's operations chief Khalid Sheikh Mohammed to prepare a devastating strike on London's Heathrow airport.

Bin Laden ordered the attack to punish British Prime Minister Tony Blair, calling him his "principal enemy", the Sunday Times newspaper reported.

The Sunday Times claimed to have seen transcripts of Mohammed's long-running interrogation. These records relate to a period of four months after his capture in Pakistan just over a year ago and indicate that Al Qaeda terrorists were sent from Pakistan and Afghanistan to work on "the Heathrow operation".

The paper also said bin Laden planned to bomb other targets.

"9/11 had originally been conceived as a two-pronged attack on five targets on the east coast of America and five on the west coast. Planners had considered targeting bridges, nuclear plants, landmark buildings such as Library Tower in Los Angeles and Sears Tower in Chicago and Hollywood studios," it quoted Mohammed as saying in the transcripts.

The transcripts also show that Mohammed, mastermind of the September 11 attacks, originally planned to hijack 10 planes and crash them into targets on the east and west coasts of America. Each interrogation is prefaced with a warning: "The detainee has been known to withhold information or deliberately mislead."

But the statements have been crosschecked with confessions of other senior Al Qaeda prisoners. This has enabled investigators to build an authentic picture of the organisation.

The claims about Heathrow by the most senior Al Qaeda member in captivity lend weight to this month's warning by Sir John Stevens, the Metropolitan police commissioner, that an attack on London is "inevitable".

Stevens said the Madrid bombings of March 11 should be a "wake-up call" to Britain and the European Union.

Like Spain, the UK has been picked by bin Laden as a target. The government said on several occasions that it has received warnings about Heathrow. But Mohammed's account is the first confirmation of an authorised plan of attack, the report said.

Mohammed told interrogators that Al Qaeda's men were given money and told to begin surveillance of the airport, assessing its weak points and finding locations from which planes might be shot down.                                 

In February 2003 -- more than a year after this directive and several weeks before Mohammed's arrest -- tanks and 400 troops surrounded the airport. Blair was accused of staging a stunt to boost support for the imminent invasion of Iraq, but insists that he had received intelligence indicating a possible attack.

"To this day we don't know if it was correct and we foiled it or if it was wrong," he said in a speech in his constituency.

Mohammed claims the Heathrow operation never advanced beyond surveillance, blaming difficulties in communicating with operatives after the Americans began to bomb Afghanistan and the Taliban government was overthrown.

Describing 9/11 as "far more successful than we had ever imagined", Mohammed said he and his colleagues were taken aback by the strength of world reaction.

"Afterwards we never got time to catch our breath; we were immediately on the run."

Key Al Qaeda people could no longer use satellite phones and had to rely on a laborious courier system. "Before September 11 we could dispatch operatives with the expectation of follow-up contact, but after October 7 (when the bombing started in Afghanistan) that changed 180 degrees. There was no longer a war room and operatives had more autonomy."