Britain warned American intelligence agents more than a year ago that the Detroit plane bomb suspect had links to extremists, Downing Street announced yesterday.
Umar Farouk Abdulmutallab was named in a file of people based in Britain who had made contact with radical Muslim preachers. The file was sent to the US authorities in 2008.
Nigerian Abdulmutallab allegedly attempted to detonate a bomb hidden in his underwear on Northwest Airlines flight 253 to Detroit on Christmas Day.
The disclosure will embarrass President Barack Obama, who is already under pressure after failures by US intelligence to identify Abdulmutallab.
It will also add to concern over the state of the "special relationship" between Downing Street and the White House following last year's dispute over the early release of the Lockerbie bomber.
The move could also be seen as an attempt to rebuff criticism from top US figures who claimed Britain had nurtured Islamic extremism.
At first it was thought that MI5 gathered only limited information on Abdulmutallab and had thus not alerted the US.
But in an official briefing, the prime minister's spokesman said that British intelligence was shared with the Americans.
He said: "Clearly there was security information about this individual's activities and that was information that was shared with the US authorities."
The spokesman added: "We are pretty certain that he was radicalised outside the UK . . .
"But it is also clear that while he was here he was attempting to make contact with people and that is the intelligence we were able to secure from the intelligence services."
Downing Street stressed that the disclosure emphasised the need for Britain and America to improve information sharing. (© Daily Telegraph, London)