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.
A Scotland Yard source said: “The great fear is Abdulmutallab is the first of many ready to attack planes and kill tens of thousands.
“We know there are four or five radicalised British Muslim cells in the Yemen.
“They are due back within months when they will be under constant surveillance.”
The 25 suspects, of Pakistani and Somali descent, were radicalised in UK mosques.
Uh, how’d that happen? I thought they were all serenely moderate.