Yard forced to arrest suspects after 'leader' seized in Pakistan

He said anti-terror police were in the middle of building a case against the plotters when news of the arrest came through.

He was referring to Rashid Rauf, 26, a Pakistani-born Briton, said to have been the "director" of the bomb plot.

Rauf was seized in Pakistan on the direction of the US authorities after they were told one of the British plotters was planning a "dummy run" to test airport security.

Mr Clarke described in The Times how he heard about his arrest on the evening of 9 August, 2006. He said: "This was not good news. We were at a critical point in building our case against them. If they got to hear that he had been arrested they might destroy evidence and scatter to the four winds. More worrying still, if they were tipped off to the arrest they might panic and mount a desperate attack."

He continued: "At Scotland Yard we decided, in a matter of minutes, that Operation Overt should be brought to an end and all 20 suspects arrested immediately.

"Detectives rushed to the Yard from all quarters, were briefed and sent out to make arrests. In the operations room, as the night wore on, the number of red dots against suspects' names, used to signify that they had been arrested, steadily grew. By morning all were in the cells."

Mr Clarke, who is now retired, said the case was a landmark conviction in terror trials stretching back to 2004.

He described how the common denominator in all of them had been Pakistan, with British terrorists travelling there for "training and tasking".