GLASGOW, Scotland -- Police said Monday they had arrested two more men as suspects in the car bomb attack on Glasgow airport as details emerged that authorities had been close on the trail of the suspects, one of whom may have been a local doctor.
Rental agent Daniel Gardiner, whose company leased a Glasgow-area home searched by police, said authorities contacted his firm just ahead of Saturday's airport attack.
Strathclyde police said two men, ages 25 and 28, had been detained under the Prevention of Terrorism Act, correcting an earlier report one suspect was 20 years old.
"This continues to be a fast-moving investigation and I am grateful to the public for their perseverance and support during these difficult times," Assistant Chief Constable John Malcolm said.
Meanwhile, British police were sifting through large amounts of evidence from the vehicles and from video surveillance of the scenes where two car bombs failed to explode in central London on Friday and two men rammed a Jeep Cherokee into the Glasgow airport's entrance the following day.
Police have arrested five other suspects while conducting raids across a country on its highest level of alert and are searching for others. None of them have been identified, but British officials have said they are hunting for what they called an al-Qaida-linked network behind the three attempted terrorist attacks.
Security in London was highly visible Monday morning, with long lines of cars forming behind police checkpoints on the London Bridge. Concrete car-blockers were in place protecting the Wimbledon tennis tournament.
"It is clear that we are dealing, in general terms, with people who are associated with al-Qaida," Prime Minister Gordon Brown said Sunday.
Brown, who replaced outgoing Prime Minister Tony Blair last week, said the threat would be "long-term and sustained" but said the country would not be cowed by the plot targeting central London and Glasgow's airport.
"We will not yield, we will not be intimidated and we will not allow anyone to undermine our British way of life," he said in a televised interview.
A British government security official said a loose U.K.-wide network appeared to be behind the attacks but investigators were struggling to pin down suspects' identities.
"These are not the type of people who always carry identity documents, or who use their real identities," the official said on condition of anonymity because of the sensitivity of the inquiries.
Gardiner, an official at the Let-It house rental agency in Glasgow, said police contacted his company on Saturday afternoon, just minutes before the airport attacks.
"A card was put through one of my colleague's door, asking if we would contact them," he said. The colleague found the note at 3:05 p.m, 10 minutes before the airport attack, Gardiner said.
"A couple of hours later, they (police) came back to us with a name, and we were able to trace their records," he said. "The police wanted to know why we had dialed a certain phone number. They had the phone records from the situation down in London."
The unidentified driver of the Jeep is being treated for serious burns at Paisley's Royal Alexandra Hospital in Glasgow, where he is under arrest by armed police. A 27-year-old man also was arrested at the airport attack by police and was being held at a high-security police station in Glasgow.
Gardiner said the suspect tenant had a six-month lease on the house in Houston, a small suburb of Glasgow.
He said the man was seen leaving the house wearing a stethoscope and was thought to be a doctor at the Royal Alexandra Hospital in Paisley on the outskirts of Glasgow. A controlled explosion was carried out Sunday on a car left at the hospital. Police said it was linked to the airport attack.
Residents of homes that were raided by police in central England and Liverpool have claimed suspects arrested were doctors or medical students. Britain's Sky News and several British newspapers also reported that two men arrested over the attacks were doctors working in British hospitals. But police in London and Glasgow have refused to comment on the claims.
Gardiner said his agency was only aware that one man was living in the rented Houston house, as it only had one tenant on their records.
Police interviewed staff at the Let-It office and took away all documentation about the tenant, he said.
On Sunday, police sealed off the address and spent the day searching the property for clues about the bomb plots.