It has emerged that the person chosen to carry out the Al-Qaeda bombing was of Middle Eastern heritage with British-Saudi nationality and secretly working for British intelligence. He ruined the terrorists' plan by handing over his explosive device -- a high-tech version of the pants bomb that failed to detonate on a jet over Detroit on Christmas Day in 2009 -- to authorities.
To mark the first anniversary of the death of ex-leader Osama Bin Laden, terrorists aimed to blow up a plane full of Americans.
MI6 was "heavily involved" in recruiting the spy, who is yet to be identified publicly, and penetrating the plot by Al-Qaeda in the Arabian Peninsula (AQAP), said sources.
Officials have long reported that AQAP has wanted to recruit Muslims with western passports for carrying out such attacks.
MI6 refused to confirm or deny involvement in the operation in Yemen.
Quoting sources briefed by Saudi counter-terror officials, US TV networks said the individual grew up in Europe. He was radicalised before being "turned" and recruited by secret agents last year.