Alarming intelligence that an attack was imminent was the trigger for police raids which captured 24 terrorist suspects, including two white converts to Islam, The Times has learnt.
Some of those detained had been under investigation before for extremist activity.
A “martyrdom video”, apparently recorded by a would-be suicide bomber, was found at one of the raided addresses, government sources said.
Last night Gordon Brown, the Chancellor, moved to freeze the assets of 19 men arrested in the raids. Several had thousands of pounds in their accounts.
US sources claimed last night that substantial sums of money had been wired from Pakistan to two of the alleged ringleaders so that they could purchase airline tickets. One report said they were planning a “dry run”.
This may have been the event that triggered the decision to arrest the suspects. Co-ordinated arrests were also made in Pakistan, including the detention of figures in the militant group Lashkar-i-Taiba.
Meetings of the Government’s Cobra emergency unit were told that the first wave of bombings was to have targeted five aircraft leaving British airports in the next few days. The destinations, US officials said, were New York, Washington DC, Boston, Chicago and Los Angeles. The plotters are said to have studied the timetables of three US airlines: American, Continental and United.
Security sources said that a second wave of attacks had been considered, with as many as 12 aircraft to be attacked.
Surveillance on internet traffic between the suspected terrorists indicated that they had considered setting off their devices simultaneously in mid-Atlantic but had also discussed trying to blow up the aircraft as they circled above the destination cities. The aim was to cause maximum death and destruction in the air and on American soil.
Paul Stephenson, Deputy Commissioner of the Metropolitan Police, said: “We are confident that we have disrupted a plan by terrorists to cause untold death and destruction and commit mass murder. This was intended to be mass murder on an unimaginable scale.”
John Reid, the Home Secretary, said that “loss of life would have been on an unprecedented scale”.
US sources said that the main fear of British authorities was that terrorists planned to hide micro-bombs in false bottoms built into opaque energy drink bottles, enabling them to still drink the contents.
The devices may have been liquid explosive but experts said that it was more likely to have been a more stable peroxide material similar to that used in the 7/7 attacks last year.
The apparent intention was to explode the device using a detonator concealed in the flash mechanism of a disposable camera to puncture a hole in the aircraft skin. MP3 players or electronic key fobs could also have been used to trigger an explosion.
Michael Chertoff, the US Homeland Security Secretary, said: “The conception, the large number of people involved, the sophisticated design of the devices that were being considered and the sophisticated nature of the plan, all suggest that this group that came together to conspire was very determined, and very skilled, and very capable.”
Mr Chertoff said that the plan had many of the characteristics of an al-Qaeda operation — a so-called terrorist spectacular aimed at mulitiple targets. He added that it was “well advanced” and “really quite close to the execution phase”.
Strict security instructions were issued to airports and airlines yesterday. They included a ban on all hand luggage with the exception of essential travel items.
Gels and liquids were strictly barred with the exception of baby milk, but parents were told that they would have to taste the contents of children’s bottles before they could take them on to aircraft.
The measures caused chaotic scenes at airports up and down the country as hundreds of flights were cancelled and many more were delayed — all at the height of the summer holiday season.
Hours before the airport clampdown, police conducted raids in North and East London, Birmingham and High Wycombe, Buckinghamshire.
The two dozen people taken into custody are being questioned at Paddington Green high security police station in West London. The majority are understood to be young British Asian men of Pakistani descent, many holding dual nationality. But residents in areas where the arrests took place identified at least one man who they said was a white British convert to Islam.
The alleged ringleaders have been under surveillance since last year, security sources said. MI5 is believed to have been alerted by suspicious activity during visits to Pakistan.
The plot, which at first was considered too far-fetched, had echoes of an al-Qaeda plan, codenamed Bojinka and discovered in the Philippines in the mid-1990s, to use explosives in bottles in attacks on aircraft.
Reports from Pakistani intelligence, suggesting the direct involvement of senior Kashmiri militants linked to al-Qaeda, convinced British intelligence that the plot had to be taken seriously. Scotland Yard’s anti-terrorist branch was brought in to the operation last December.
“We have been looking at meetings, movements, travel, spending and the aspirations of a large group of people,” said Peter Clarke, Deputy Assistant Commisioner and head of the Anti-Terrorist Branch. “This has involved close co-operation, not only between agencies and police forces in the UK, but also internationally.”
A number of events are understood to have convinced the counter-terrorist agencies to act. A telephone call about the alleged plot was intercepted, internet communication increased noticeably and two men under surveillance disappeared off the intelligence radar. However, security sources indicated that the key event — thought to be the transfer of funds — had taken place overseas. “It was very close, and it was too risky to allow the surveillance operation to go on for any longer,” one source said.
Mr Reid, who had chaired meetings of Cobra through the night, said that all the main players in the alleged conspiracy had been traced and arrested. And a Scotland Yard source said: “We have arrested all our targets, there is no one significant outstanding.”
However, ABC, the US television network, reported sources in Washington saying that five suspects were still at large.
Police teams were continuing to search business and residential properties — including lock-up garages in the Small Heath area of Birmingham. A search was also under way in an area of woodland in High Wycombe. Scotland Yard declined to say if any explosive materials had been found.
Mr Reid said that he had raised the terrorist threat level to “critical”, suggesting that an attack in the UK is imminent, adding that he was erring on the side of caution.
Downing Street said that Tony Blair, on holiday in the Caribbean, had been aware of the operation for several weeks.
WHAT THEY SAID
‘Today marks the culmination of one phase of a major operation that has lasted several months, and will last long into the future’
Peter Clarke, Metropolitan Police anti-terrorist branch
‘We are involved in a long, wide and deep struggle against very evil people’
John Reid, Home Secretary
‘Planes remain vulnerable. In the coming weeks terrorists will be thinking of something else to do that we have no idea about’
Peter Neumann, Centre for Defence Studies, King’s College, London
These are the names of 19 suspects reportedly being held by the police after the foiled plot and whose assets the Treasury has sought to have frozen.
Umir Hussain, 24, London E14
Muhammed Usman Saddique, 24, London E17
Waheed Zaman, 22, London E17
Assan Abdullah Khan, 22, London E17
Waseem Kayani, 28, High Wycombe
Waheed Arafat Khan, 24, London E17
Cossor Ali, 24, London E17
Tayib Rauf, 21, Birmingham
Ibrahim Savant, 26, London E17
Osman Adam Khatib, 20, London E17
Shamin Mohammed Uddin, 36, Stoke Newington
Amin Asmin Tariq, 23, London E17
Shazad Khuram Ali, 27, High Wycombe
Tanvir Hussain, 24, London E10
Umar Islam, 28, (born Brian Young) High Wycombe
Assad Sarwar, 25, High Wycombe
Abdullah Ali, 26, London E17
Abdul Muneem Patel, 17, London E5
Nabeel Hussain, 21, Waltham Forest