Four suspects were in police custody Sunday - and a fifth man was under guard in hospital - after a flaming Jeep crashed into a Scottish airport on Saturday and two car bomb plots were foiled in central London on Friday.

Police said Sunday's search was taking place in a residential area about seven miles west of central Glasgow, about a mile from the airport. The area around a two-story house in Houston, a small town just outside Glasgow, was cordoned off.

Scotland Yard said two people were arrested early Sunday on a major highway in Cheshire, northern England, in a joint swoop by specialist officers from London and Birmingham. Another person was arrested overnight in Liverpool, police said.

Police offered no further details on those arrested.

In Scotland, officers arrested two men - one of them badly burned - after a Jeep Cherokee rammed into Glasgow airport and burst into flames. The green SUV shattered glass doors at the terminal entrance, stopping within yard of where passengers were lined up at check-in counters.

Police and security officials said the attacks were clearly linked, adding all three vehicles carried large amounts of flammable materials - including gasoline and gas cylinders. The chaos over the past two days has raised fears that the type of car bomb attack that have become commonplace in Iraq has now reached European shores.

Britain on Saturday raised its terror alert to "critical" - the highest possible level - and the Bush administration announced plans to increase security at airports and on mass transit.

In an interview on British Broadcasting Corp. TV Sunday, Brown, who replaced Tony Blair as Britain's prime minister last week, said Britons face a "long-term and sustained" terrorist threat.

He said that Britain's message to the terrorists must be: "We will not yield, we will not be intimidated, and we will not allow anyone to undermine our British way of life."

Brown said it is "clear that we are dealing, in general terms, with people who are associated with al-Qaida."

In a column in Sunday's News of the World newspaper, Lord Stevens, London's former police chief and Brown's new terrorism adviser, said: "This weekend's bomb attacks signal a major escalation in the war being waged on us by Islamic terrorists."