Home Secretary Jacqui Smith said at least 19 locations were searched as part of the "fast-moving investigation."
Late Monday, police announced the arrest of an eighth suspect, a man, in the failed attacks. Authorities would not disclose where the arrest was made, but the British Broadcasting Corp. reported the man was detained overseas. Seven others, including a woman, were arrested earlier.
Vigilance was high less than a week before the anniversary of the deadly July 7, 2005, London transit bombing. Those attacks were largely carried out by local Muslims, exacerbating ethnic tensions in Britain.
In the latest attempted attacks, two car bombs failed to explode in central London on Friday and two men rammed a Jeep Cherokee loaded with gas cylinders into the entrance of Glasgow International Airport on Saturday.
(Mohammad abu Ghosh ~ Associated Press)
Police said one man arrested in Glasgow is Bilal Abdulla.
According to the British General Medical Council's register, a man named Bilal Talal Abdul Samad Abdulla was registered in 2004 and trained in Baghdad. Staff at Royal Alexandra Hospital said one suspect was a doctor of Middle Eastern or Iraqi origin who worked there.
A second man arrested late Saturday on a highway in central England is Mohammed Jamil Abdelqader Asha, according to a police official who was not authorized to publicly disclose the details and spoke on condition of anonymity.
A Jordanian official said British authorities had contacted the Jordanian Embassy in London to say Asha, who reportedly worked at a hospital in central England, was a possible suspect. The official said Asha was a native Palestinian who carried a Jordanian passport.
In Jordan, Asha's brother Ahmed said he had heard the media reports and said his 26-year-old sibling "is not a Muslim extremist, and he's not a fanatic."
"It's nonsense because he has no terror connections," he said.
A British government security official said a loose U.K.-wide network appeared to be behind the London and Glasgow attacks, but investigators were struggling to pin down suspects' identities.