Of the doctors held, police sources named one as Bilal Abdulla, who qualified in Iraq in 2004, and another as Mohammed Asha, who qualified in Jordan the same year. Asha's wife was also among those arrested.
According to the Muslim News, a Web site that follows the British Muslim community, another of those seized in Britain was also a doctor. It quoted a colleague of the man as saying he had
come to Britain from Bangalore in India.
Britain has seen a marked increase in terrorism-related attacks since the Sept. 11 strikes on the United States and since it joined U.S. forces in invading Iraq in 2003.
But previous attacks, including one on London's transport system in July 2005 which killed 52 people, have tended to involve radicalised, British-born Muslims, not educated attackers from overseas, security experts say.
Police cordoned off a hospital in Paisley, a town just outside Glasgow, on Monday and carried out several controlled detonations.
The hospital, the Royal Alexandra, is where Abdulla worked, staff said, and where he is also believed to be being treated for severe burns after taking part in the attack on Glasgow airport, when his vehicle was turned into a fireball.
Fearing further attacks, police banned cars and other vehicles from directly approaching airports and security measures were stepped up across the country as authorities kept
the threat level at "critical," the highest rating.
The series of foiled and actual attacks pose a test for Prime Minister Gordon Brown, a Scot who replaced Tony Blair only last week and who has come under pressure from some quarters to change policy on Iraq and withdraw British troops.
Blair was known for an aggressive stance on security and a foreign policy that strongly supported the United States in Afghanistan and Iraq. The bombers who struck London in 2005 said in videos they were punishing Britain for Blair's policies.
Home Secretary (interior minister) Jacqui Smith said Britain was facing a "serious and sustained threat of terrorism" and urged the public to remain alert.
Addressing parliament on Monday, she praised the security services for their quick work in rounding up suspects but said a threat remained.
In Amman, Jordan, the father of Mohammed Asha described his son as a good Muslim, not a fanatic, and expressed incredulity that he could be involved in an al Qaeda-style bomb plot.
"I am sure Mohammed does not have any links of this nature because his history in Jordan and since he was a kid does not include any kind of activity of this nature," he said.
He said Mohammed and his wife were happy with their life in Britain and had had a son in the country about 18 months ago.