A four-wheel-drive vehicle crashed into the main terminal at Glasgow airport on Saturday and exploded in flames, a day after police foiled a possible al Qaeda plot to detonate two car bombs in central London.
A Glasgow police spokeswoman said there were no immediate reports of any injuries and said the blaze was under control.
Witnesses told the BBC that the vehicle, a Land Rover or a Jeep Cherokee, had exploded shortly after crashing into the glass front doors of the terminal, and said there was a heavy stench of petrol.
It raced across the central reservation and went straight into the building, said taxi driver Ian Crosby outside the terminal.
Crosby said a stocky Asian man had got out of the car and was quickly wrestled to the ground by bystanders.
It would appear to me to have been a deliberate attack. I think this was a terrorist attack, Crosby said.
In London, police scoured hours of CCTV footage and extra squads were deployed on the streets, particularly around landmarks such as the Houses of Parliament after Friday's failed car bomb attacks in the centre of the city.
However, tourists and Londoners appeared largely unperturbed, going about their business as usual.
An intensive counter-terrorism investigation was launched after the discovery in the early hours of Friday of a metallic green Mercedes packed with up to 60 litres of fuel, several gas canisters and a large quantity of nails.
The vehicle was parked outside the Tiger Tiger night club in the busy theatreland district of London, and aroused suspicion only after ambulance workers, treating someone else, thought they had noticed smoke inside the vehicle.
A mobile phone, which security experts believed might have been a detonation device, was left inside the fume-filled car.
A second Mercedes packed with gas and nails was later found to have been parked just a few hundred yards from the first.
Police said the two vehicles were clearly linked. Both bombs were quickly defused but, had they gone off, would have caused significant injuries and deaths, police said.
JULY 2005 ATTACKS
The thwarted bomb plot came to light two years after a coordinated attack by suicide bombers on London's transport system killed 52 commuters. It appeared to have similarities to an earlier plot in which an al Qaeda militant planned to blow up gas-filled bombs inside limousines in London.
Plans for policing of public events in the coming 10 days were reviewed to ensure public security, including a Gay Pride parade in London on Saturday, the Wimbledon tennis tournament and a concert for Princess Diana on Sunday.
Appropriate policing will be in place for all events, a police spokeswoman said. Safety and security is our number one priority.
Despite the continuing threat, tourists were stoical.
You could be safe anywhere or you could be safe nowhere. It hasn't put me off traveling here, said Ivonne Geller, 49, a tourist from Mexico strolling outside the Tiger Tiger club.
I just feel angry about the methods of these people who try to harm innocent people.
Intelligence sources believe there is a growing probability that the plot was hatched by an al Qaeda-style group.
The feeling it is Islamist, rather than the other possibilities, is very quietly growing stronger, a source said.
The area of London where the car bombs were left, known as Haymarket, is one of the busiest in the capital and one of the most intensely monitored by CCTV surveillance.
Police said they were studying hundreds of hours of footage in the hunt for possible suspects. The U.S. television channel ABC reported that a crystal clear image of a suspect had been found, but British police would not confirm that.
(Additional reporting by Avril Ormsby)