Cops fear that 25 British-born Muslims are plotting to bomb Western airliners.
The fanatics, in five groups, are now training at secret terror camps in Yemen.
It was there London-educated Umar Abdulmutallab, 23, prepared for his Christmas Day bid to blow up a US jet.
The British extremists in Yemen are in their early 20s and from Bradford, Luton and Leytonstone, East London.
They are due to return to the UK early in 2010 and will then await Internet instructions from al-Qaeda on when to strike.
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Meanwhile, US-bound passengers interviewed at JFK yesterday said they found themselves subjected to increased security.
New measures included additional pat-downs and prohibitions against leving one’s seat during the last hour of a flight and against placing a pillow or blanket on their laps.
“I was a little confused about not having blankets and pillows — but if it’s for safety, then it’s all for the best,” said Marni Blitz, who landed on a flight from Zurich.
With Rueven Fenton in New York.