Government sources indicated to The Times that the apprehension of Rashid Rauf was the key event that forced British police to raid addresses in London, Birmingham and High Wycombe. One of those arrested in Birmingham was Rauf’s brother, Tayib, 21.

Police brought the raids forward because they were concerned that the alleged plotters would realise they were under surveillance once they lost contact with a central figure in their plans, and either go into hiding or carry out an attack.

In a separate development, Scotland Yard is investigating possible links between the men arrested on Thursday and other British terrorists, including the July 7 bombers. They are concerned that some of those now in custody visited Pakistan last year at the same time as two of the London bombers. Pakistani intelligence sources are examining whether any of those arrested on Thursday attended the same madrassa, or religious school, as the 7/7 bombers..

Searches after Thursday’s arrests had uncovered material which could be used in bomb making, The Times was told by security sources last night.

Rashid Rauf left Britain in 2002 after the murder of his uncle Mohammed Saeed, 54, who was stabbed to death in Birmingham in April of that year. Pakistani officials said that Rauf had forged links with militant groups and received explosives training at an al-Qaeda camp. The Foreign Ministry said: “A key person arrested is British national Rashid Rauf”.

West Midlands Police said that the home of the Rauf family, at St Margaret’s Road in Ward End, Birmingham, had been searched in 2002 in connection with the Saeed murder inquiry. Rashid Rauf has not been arrested or charged with his uncle’s murder.

The Pakistani authorities have made several more arrests which they said were directly connected to the airline plot. They said that one was a British national.

Another of those detained is understood to be Matiur Rehman, 29, previously identified by Pakistani intelligence as a senior al-Qaeda operative and linked to an assassination attempt on President Musharraf. The Pakistani Foreign Ministry added: “There are indications of an Afghanistan-based al-Qaeda connection.”

John Reid, the Home Secretary, has thanked the Pakistani Government for its assistance. He said the threat level would remain at “critical”.

Police have been granted an extension until August 16 to question the suspects. They can in theory hold them for 28 days before charging or releasing them. One person has been released without charge.

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