Two weeks ago, the agent walked away from al-Qaeda with the device he was supposed to use in an attack on US-bound aircraft.
He traveled to the United Arab Emirates and then to Saudi Arabia, with the device before handing it over to his British handlers.
He was also able to give information which led to a CIA drone strike on Sunday which killed Fahd al-Quso, AQAP’s director of external operations.
However al-Asiri was not there and remains at large, frustrating efforts to kill him. The mission is particularly sensitive because British agents are not supposed to give “targeting information” for lethal operations.
The underpants device was handed to the FBI laboratories in Quantico, Virginia, which examined a similar device used by Umar Farouq Abdulmutallab on a trans-Atlantic airliner to Detroit on Christmas Day 2009.
The FBI has discovered that Asiri had refined the prototype he first developed for use by his own brother in a suicide operation three years ago so that it could be detonated in two separate ways.
The British security services are thought to be unhappy that their role has become known, fearing it may jeopardise the recruitment of future agents who are given anonymity even after they die by the service. Whitehall sources refused to comment.
Sir John Sawers, the chief of MI6, said, in a rare public speech two years ago: “Our agents are the true heroes of our work. They have their own motivations and hopes. Many of them show extraordinary courage and idealism, striving in their own countries for the freedoms that we in Britain take for granted
“They receive recognition for their achievements only within the confines of the service. You don’t know them, but I do. It is an honour to lead them.”
The operation was originally made public in a leak to the US news agency the Associated Press.
The Daily Telegraph reported MI6’s involvement on Tuesday but the key role they played was confirmed only on Thursday from a source briefed by Saudi Arabia counter-terrorism officials, who spoke to CNN.
