By Ian Stewart
The Associated Press
GLASGOW, Scotland — British police raided buildings near Glasgow and in central England and made a fifth arrest on Sunday, as the hunt intensified for suspects in the fiery attack on the Scottish city's airport and foiled car bombings in London.
The terrorist threat that Britain faces is "long-term and sustained," Prime Minister Gordon Brown said in a nationally televised interview. It is clear, he said, "that we are dealing, in general terms, with people who are associated with al-Qaida."
On Friday, police thwarted an apparent plot to set off a coordinated bomb attack in central London when an ambulance crew outside a nightclub spotted smoke coming from a Mercedes that was found to be rigged with explosives. They found a second Mercedes filled with explosives hours later.
And on Saturday, two men rammed a flaming Jeep into the main entrance of Glasgow airport, shattering the glass doors and sparking a raging fire just yards away from people lined up at check-in counters.
Britain raised its terror alert to "critical" — the highest possible level — and the U.S. homeland security chief, Michael Chertoff, said Sunday that air marshals would be added to overseas flights.
"We are learning a great deal about the people involved in the attacks here in Glasgow and in the attempted attacks in central London. The links between them are becoming ever clearer," said Peter Clarke, head of Scotland Yard's counterterrorist unit.
"I'm confident, absolutely confident, that in the coming days and weeks we will be able to gain a thorough understanding of the methods used by the terrorists, the way in which they planned their attacks and the network to which they belong."
The two men from the Glasgow attack were in police custody Sunday, the apparent driver under guard in Royal Alexandra Hospital with severe burns. Glasgow's Assistant Chief Constable John Malcolm said they were the only two in the Jeep.
A road in front of the hospital was closed Sunday as police carried out the controlled explosion, and ambulances were taking emergency patients to another hospital, police said. All other wards were open, police said. No explosives were found.
Early Sunday, police arrested two people — a 26-year-old man and a 27-year-old woman — on a major highway in Cheshire in a joint swoop by officers from London and Birmingham. Staffordshire Police Chief Superintendent Steve Loxley said officers raided addresses in the central town of Newcastle-Under-Lyme near the highway where the two were arrested.
A fifth suspect, a 26-year-old man, was arrested in Liverpool, and two homes were searched there, police said.
"Al-Qaida has imported the tactics of Baghdad and Bali to the streets of the UK," said Lord Stevens, a former London police chief and Brown's terrorism adviser.
The new terror threat presents Brown with an enormous challenge early in his premiership — at a time of already heightened vigilance one week before the anniversary of the July 7, 2005, London transit attacks.
Brown, a Scot who replaced Tony Blair as prime minister on Wednesday, urged Britons to remain "constantly vigilant" about security. He said "Everything is being done in our power ... to protect people's lives."
"We will not yield, we will not be intimidated, and we will not allow anyone to undermine our British way of life," he told the British Broadcasting Corp. in a TV interview.
Glasgow police chief Willie Rae said a suspicious device was found on a man wrestled to the ground by officers at Glasgow airport and hospitalized in critical condition with severe burns. Despite speculation about a suicide belt or explosives, police later said the item had been found to be safe.
John Smeaton, who saw the attack, said the man shouted "Allah, Allah" as he was detained.
Police did not say whether the SUV that struck Glasgow airport was carrying explosives, but photographs of forensic officers inspecting the charred vehicle on Sunday showed several gas canisters next to it.
Glasgow airport reopened Sunday, although some flights were canceled. Cars were not allowed to drive up to the terminal building, and a tow truck arrived to remove the crashed Jeep.
Security also was stepped up at three of London's main airports — Heathrow, Gatwick and Stansted — as officials severely restricted access to drop-off and pickup areas used by cars, searched some vehicles, and urged people to travel to airports by public transportation.
In Washington, Chertoff said the U.S. was satisfied with its current terrorism alert level and acknowledged potential al-Qaida links to the plots in Britain. In response to the British attacks, U.S. airports and mass transit systems were tightening security ahead of America's Fourth of July holiday.
Last year, a 35-year-old British convert to Islam was convicted of plotting to bomb several U.S. financial targets and luxury London hotels with a plot that called for using limousines packed with gas tanks, napalm and nails.
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In April, accused members of an al-Qaida-linked terror cell were convicted of conspiring to blow up the Ministry of Sound nightclub, one of London's biggest music venues.