Terrorists plotting to blow up passenger jets in mid air could have been just two days away from launching their mission to commit "mass murder on an unimaginable scale".
Their plan was to detonate liquid-based explosive devices smuggled in hand luggage on as many as ten aircraft leaving UK airports for the US. If successful the plan, which bore the hallmarks of an al Qaida plot, would have been a terrorist 'spectacular' on a par with the 9/11 atrocity.
A joint investigation by MI5, West Midlands Police and the Metropolitan force reached a critical point on Wednesday night and anti-terror officers swooped in the early hours of yesterday, arresting 24 young Britons of Pakistani origin in Birmingham, London, and the Thames Valley.
Home Secretary John Reid said that if the plot had succeeded, it would have caused death on an "unprecedented scale".
There were also claims last night that a martyrdom video, typically made by suicide bombers and released after their deaths, had been discovered at one of the addresses raided by police.
Yesterday's events prompted the British authorities to raise the terrorist threat level to critical for the first time.
Yesterday, residents in Birmingham's Alum Rock and Ward End, where two people were arrested during the dawn raids, were struggling to understand how their neighbours could be implicated in one of the largest modern terror plots to be discovered on British soil.
The men, who locals believe were brothers, were said to have grown up in a religious but otherwise unremarkable family. According to neighbours, their hardworking father ran a cake shop. "I cannot see the sons sending money to fund terrorism," said one former schoolmate. "Even the bad people in the area are not that bad."
Believed to have lived in Ward End for around 12 years, the family were known to have held lessons on the Koran and prayer for local children in a purpose-built classroom in their back garden in St Margaret's Road. A commercial property in Belcher's Lane, Alum Rock, allegedly used by the family, was also raided by officers.
Yesterday, US President George Bush was in no doubt a major terrorist threat had been foiled, saying the plot was a stark reminder the West was "at war with Islamic fascists who will use any means to destroy those of us who love freedom".
In response to the threat, stringent new security measures were imposed at all UK airports, causing widespread chaos. A ban on hand luggage along with other checks led to huge departure-hall queues, including at Birmingham International, with scores of flights cancelled across the country.
Police revealed yesterday's arrests followed an "unprecedented level of surveillance" stretching back to December. Security sources confirmed the attack could possibly have been mounted within a couple of days.
Police were last night continuing to search several addresses, including properties in High Wycombe and Walthamstow. Sources said police found "a number of things that are causing interest".
It is thought the would-be terrorists planned to carry explosive material and detonators on to planes disguised as drinks and electronic devices; the separate components would have been assembled in mid flight.
US air marshals are being sent to the UK for extra security on flights bound for America.
"We are involved in a long, wide and deep struggle against very evil people," Mr Reid said.