Police are confident that all the main players in the alleged airliner bomb plot have been accounted for, the British Home Secretary said today.
John Reid said had the plot been carried out the loss of life would have been on “an unprecedented scale”.
He told a news conference that the police operation was complex and ongoing, and that the decision to act overnight had been taken with the full knowledge of the Prime Minister and Deputy Prime Minister.
“The police, working with the Security Service, MI5, have carried out a major counter-terror operation overnight to disrupt an alleged plot to bring down a number of aircraft through mid-flight explosions.
“Had this plot been carried out the loss of life to innocent civilians would have been on an unprecedented scale.”
Mr Reid added: “While the police are confident the main players have been accounted for, neither they or the (British) government are in any way complacent.
“This is an ongoing and complex operation.”
Mr Reid said he had chaired two Cobra meetings of senior officials, police and security service personnel overnight and this morning.
Britain’s law enforcement agencies were “working round the clock” to prevent any further terrorist activity, he said.
Tony Blair had briefed the US President on the operation and Britain had been in touch with the US Homeland Security Department and its transport department, he added.
“We all believe we have taken the necessary precautionary measures to protect the public, both by the actions we have taken and by the means of that threat level, for the time being at the highest possible level,” Mr Reid said.
British Transport Secretary Douglas Alexander said the British government had been left with no alternative but to implement extra security on flights.
“The seriousness of the threat gave us no choice but to require these stringent measures to be implemented.”
Mr Alexander said he had been in continual contact with aviation industry figures.
He urged passengers to “show understanding” through the inevitable difficulties they would face with their journeys.