A British national played a key role in thwarting an al-Qaida underwear bomb plot, according to U.S. sources.

The man posed as a suicide bomber to foil the plot, devised by the terrorist group's Yemeni offshoot, al-Qaida in the Arabian Peninsula, and is understood to be a British citizen, possibly of Saudi origin, CNN and MSNBC claimed.

The plot revolved around putting a suicide bomber on a U.S.-bound plane. He would be wearing an upgraded, non-metallic version of the underwear bomb used in a failed attack on Christmas Day, 2009.

The individual chosen for the attack, who was initially believed to have been radicalised in Europe but was actually an informant working in cooperation with British spy agencies, handed the bomb over to the authorities.

The plot's foiling was originally hailed as a victory for the CIA and allied foreign intelligence services, with key help from Saudi Arabia. However, the new information appears to show that British intelligence played a vital role.

Bomb plot
The al-Qaida bomb plot is thought to have been foiled with the help of British intelligence (Reuters)

A US drone attack over the weekend, which killed al-Qaida operative Fahd al-Quso, is thought to have been a direct result of information from the agent, according to the Guardian. MI6 and MI5 agents are banned from missions leading to assassinations.

The Associated Press was made aware of the underwear plot last week but did not publish details until Monday at the request of the White House over operational security.

The Foreign Office declined to confirm or deny the involvement of British intelligence.