Barack Obama is under pressure to disclose what information MI5 passed to the American authorities about the Detroit bomber after Downing Street disclosed that a file had been "shared" with the CIA in 2008.
After initially (denying) "lying" that they had received British intelligence, senior American sources confirmed last night that they were "reviewing" what British information had been received on Umar Farouk Abdulmutallab.
The admission is embarrassing for the White House and threatens to provoke a rift with Gordon Brown. The conflicting briefing over the shared intelligence also suggests that the transatlantic relationship may have weakened in recent months.
Confirmation that Abdulmutallab's name was passed to the US in 2008 would be a major blow to Mr Obama, although it could also open up accusations that George W Bush's administration failed to collate intelligence properly.
The Prime Minister's spokesman disclosed on Monday that MI5 information had been shared with the Americans more than a year ago. Alan Johnson, the Home Secretary, confirmed this in the House of Commons yesterday. The information is understood to have detailed Abdulmutallab's contacts with radical preachers but did not give warning that he might be a terrorist threat.
White House sources are thought to be furious over the British intervention, with Mr Obama already under pressure over intelligence failures concerning the thwarted attempt to blow up the US airliner.
Yesterday, the Prime Minister's spokesman played down the rift. Both British and American officials insisted the intelligence would not have prevented the attempted attack.
However, there are growing questions as to why Abdulmutalab was granted a US visa and why his name was not on a US watch list.