Suspected terrorists were planning to unleash a wave of "apocalyptic" attacks on land and air, using an arsenal of bombs and weaponry, including firearms, investigators have discovered.
Police and intelligence sources have indicated that the alleged plot which was thwarted last week was targeted at the UK, as well as at airliners heading for the US, and could have caused devastating loss of life and destruction on the British mainland. One Whitehall source said "many dozens" of plots were under investigation, involving "hundreds" of suspects.
According to one report last night, al-Qa'ida's leader in Britain could have been held in the raids. But security sources estimate that as many as 1,200 people here are actively involved with terrorism, and that the country is still under "very severe" threat from other potential terrorist plots. This, they added, explained why there were no immediate plans to lower the current national threat assessment from "critical", its highest level.
Last night, 23 people were still being held under terror laws at Paddington Green police station, west London, and other police stations in what has been described as the biggest operation carried out by police to prevent a potential terror attack. Legal sources said that most would be detained for the full 28 days allowed under the terror laws, before being charged. Detectives were preparing for "a long haul", police sources said.
Sources have told The Independent on Sunday that intelligence officers are aware of several active "jihadi" cells around the country including one in east London thought to be unconnected to the suspects arrested last week. Investigators said surveillance in progress since the July 2005 bombings in London had identified the locations of explosives and weapons in quantities sufficient to commit wide-scale atrocities.
The alleged plot uncovered last week was said to involve apparently innocuous home-made liquid explosives being carried on to aircraft, and then turned into bombs using electronic devices such as iPods or cameras. Last night it was reported that police had recovered scores of bottles containing peroxide, a chemical which can be used to make bombs, from a recycling bank in High Wycombe.
The IoS has also learnt that British security officers are to investigate the availability over the internet of so-called binary explosives that can be made easily from two harmless substances. Experts were alarmed to discover that a Canadian company is openly selling an explosive made simply by combining a liquid with a powder in a plastic bottle, and then attaching a detonator.
John Reid, the Home Secretary, told police chief constables yesterday that there was no room for "complacency or self-congratulation". He added: "As I have said all along, no one should be under any illusion that the threat ended with the recent arrests. It didn't."
* The Sunday Telegraph reported that it had uncovered a dossier of " extremist Islamic literature" at London Metropolitan University, one of whose students was arrested last week. Material included documents advocating jihad and a pamphlet on how to deal with approaches from the security services.