The man dispatched by Al Qaeda to blow up a US-bound passenger airliner with a bomb feared to be undetectable was a Saudi double agent.

Foiling the plot was a Saudi-run operation, with the agent identified and recruited by the Saudi interior ministry's counter-intelligence agency using extensive tribal and family ties in Yemen.

In what a former CIA counter-terrorism agent described last night as a stunning coup for Saudi intelligence, their agent delivered three knock-out blows to Al Qaeda in the Arabian Peninsula.

Firstly, he prevented the attack. Secondly, he delivered the explosive device to analysts intact, providing crucial new insight into AQAP's latest bomb-making technology. And thirdly, he identified the leaders of the AQAP cell who planned the bombing.

The result was a US drone strike in Yemen on Sunday that killed Fahd Mohammed Al Quso, believed to be the cell leader and also wanted for the bombing of USS Cole in Yemen in 2000.

The Saudi double agent is understood to have escaped to safety in Saudi Arabia via the UAE, and his close relatives are also believed to have been brought out.

Overall, it is a "stunning" success, a former CIA counter-terrorism agent with operational experience in the Middle East told The National yesterday.

"I've never heard of such a coup. This is as big as it comes in the post-September 11 hyped-up environment in which [intelligence agencies] operate today. It doesn't get any better."

It is a particular coup for Saudi intelligence, he said, as such "intelligence diplomacy" links Saudi Arabia and the US "even more tightly at the hip", and constricts any possible criticism in Washington of domestic Saudi human-rights issues.

It also sends the message to other countries that "if we collaborate in the war on terror, the US will turn its attention away from our internal affairs", a card Israel plays "most brilliantly" in deflecting US attention from its behaviour in the occupied territories, the former agent said.

The operation was not only a collaboration between Saudi and US intelligence, however. It also involved the highest levels of the Yemeni government, according to a government official in Sanaa.

The official told The National that Abdrabu Mansur Hadi, the Yemeni president, was told about the plot but that Yemen's two intelligence agencies were kept in the dark out of concerns that the information might find its way to Al Qaeda.

"[Saudi and US intelligence] were concerned about the disclosure of the information on this thwarted plot because the attacks of Al Qaeda on the army in the south - slaughtering soldiers on a mass scale - demonstrate that the terrorist organisation either has eyes in the army or is finding facilitation from army officers," the official said.

US officials say the bomb is probably the work of Ibrahim Hassan Al Asiri, who they accuse of building the original underwear bomb, which failed to detonate aboard a plane over Detroit in 2009.

He is also suspected of being the bomb-maker behind the failed plot to detonate explosives hidden in toner cartridges in printers on a plane to Chicago that was intercepted in Dubai in 2010.

Analysts believe the latest bomb was more sophisticated, built without any metal components and designed to pass undetected through airport scanners.

The Central Intelligence Agency was kept in the loop throughout the Saudi double-agent operation, but there is anger in the US that the plot was leaked from the CIA last week, becoming public knowledge on Monday.

The leak might discourage foreign intelligence services from co-operating with the US on risky missions in the future, said Peter King, a Republican congressman and chairman of the House Homeland Security Committee.

"We are talking about compromising methods and sources and causing our partners to be wary about working with us," said Mr King, who called the bomb plot "one of the most tightly held operations I've seen in my years in the House".

US officials planned to investigate the source of the leak.

In any case, the story will work well for Barack Obama, the US president, in an election year, the former CIA agent suggested. The Obama campaign has already made the killing of Osama bin Laden a prominent plank of the US president's re-election bid.

The latest operation will only bolster Mr Obama's "tough guy" image, the agent said.