Security officials in Britain were unaware of the alleged airlines terror plot until a Birmingham man arrested in Pakistan revealed the details, sources have claimed.
Rashid Rauf, a 25-year-old who left Birmingham in 2002, broke down during questioning following his arrest in Pakistan on August 4, according to reports.
British security officials had asked Pakistani security forces to trail him for two weeks before his arrest more than a week ago.
However, US sources said American and British security officials were not aware of the full extent of the plan to blow up transatlantic airliners until Rashid was detained.
"When they interrogated Rauf he broke. He told them what we believe was not even in the knowledge of the US and the British - that they were actually planning to blow up airliners," the officials said.
Pakistani authorities said an intercepted telephone call from Karachi to Britain that urged plotters to go ahead with attacks played a crucial role in foiling the alleged terror plan.
The arrest of Rauf prompted an unidentified associate of his to make the call to one of the suspects subsequently arrested in Britain.
This also led to British security forces carrying out a series of raids on Thursday morning on plotters who had long been under surveillance.
"This telephone call intercept in Karachi and the arrest of Rashid Rauf helped a lot to foil the terror plan," a senior Pakistani security official said.
However, the official would not confirm when exactly the call was intercepted.
Rashid Rauf has been described by senior Pakistani officials as having ties with al Qaida and being a "key" suspect.
He is the brother of Tayib Rauf, a Birmingham man and one of 24 people arrested last week over the alleged plot to use liquid-based bombs to blow aircraft in flight.
Rashid made a brief appearance before a magistrate in Pakistan on Saturday before being remanded in custody. He is also believed to be wanted in the West Midlands for questioning by police investigating the murder of his uncle, Mohammed Saeed, in April 2002.
The 54-year-old was stabbed to death just yards from his home in Alum Rock where he later died in front of his wife and two children.
It has also emerged that the Rauf family home, in St Margarets Road, Ward End, was previously raided by detectives investigating the murder of black IT worker Isiah Youngsam after the recent Lozells riots. No arrests were made or weapons found at the property.
Pakistani investigators said they were now closely examining Rashid's links to Afghanistan.
"They managed to locate Rauf from a hideout in Bahawalpur. He was staying at a former Afghan jihadi's house, it was a very swift raid and not even the police were involved," a security official said.
However, Afghanistan's foreign ministry last night denied any Afghan al Qaida connection to the alleged plot.
Meanwhile, sources in Pakistan rejected reports in Britain that a top Pakistani al Qaida militant named as Matiur Rehman was involved in the conspiracy and had been arrested.
"Rehman is not a mastermind of the UK bombing plot, his name has not yet figured in the investigations," a security official said, adding that Rehman was wanted for an assassination attempt on President Musharraf of Pakistan."