GLASGOW, Scotland — Police said today 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 this 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.