Homes and businesses across England are being searched and 21 people questioned after a terror plot to blow up planes from the UK to US was disrupted.
Police are convinced they have the key players in custody, but a much wider investigation is only just beginning.
Peter Clarke, the head of Scotland Yard's anti-terrorist branch, said the network involved was large and global.
And US Homeland Security Secretary Michael Chertoff said the plot was "in some respects suggestive of al-Qaeda".
Security chiefs, who had had the group under surveillance for some time, said they were close to putting their plan - which police said would have caused "mass murder on an unimaginable scale" - into action.
Sources in the UK have confirmed that they believe an attack may have been imminent - possibly in the next few days
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http://news.bbc.co.uk/1/hi/uk/4780815.stm