LONDON -- British police arrested a fifth suspect yesterday in their nationwide manhunt for the perpetrators of failed bomb attacks in central London and at the Glasgow, Scotland, airport.
Authorities also searched a suspicious vehicle outside the Scottish hospital where they had taken one of the Glasgow suspects, who suffered severe burns when he drove a Jeep Cherokee into the glass entrance to the main airport terminal Saturday.
Security officers also temporarily shut down a portion of London's Heathrow Airport yesterday to investigate reports of a suspicious package.
The new arrest came in Liverpool, where a 26-year-old man was taken to the high- security Paddington Green police station in London. Liverpool police said the arrest was made in connection with the two car bombs discovered Friday in central London.
TV reports said that one key suspect remained at large.
New clues were surfacing almost hourly, and links between the London and Glasgow incidents were "becoming clearer," said counterterrorism chief Peter Clarke, who briefed reporters in the Scottish city.
Prime Minister Gordon Brown, a Scotsman, urged British residents to remain calm yesterday, even as the nation's terror alert rating remained at "critical," the highest level. In the first television interview of his premiership, Brown told the BBC that he recognized the present terror threat as "long-term and sustained."
"[But] it's very important," he added, "that we the British people send a message to terrorists that they will not be allowed to undermine our British way of life."
Tens of thousands of people, undeterred by the threat of additional attacks, attended a London concert yesterday that was organized by Prince William and Prince Harry as a tribute to their late mother, Diana, Princess of Wales, on the day she would have turned 46. The concert, which featured performances by artists Duran Duran and Elton John, was guarded by armed police officers. Normally a rarity in Britain, armed officers patrolled public places across London yesterday and are expected to remain on the streets indefinitely.
Security was stepped up at British airports and train stations, and spot checks on cars began around the country.
In Glasgow, Scottish police continued to hold the two men who drove the Jeep that exploded as it hit the doorway to Terminal One of Glasgow International Airport. The driver was in a critical condition in the city's Royal Alexandra Hospital, suffering from burns over much of his body. The passenger is in police custody in Glasgow.
According to Scottish First Minister Alex Salmond, indications were "that these people had not been in Scotland for any length of time."
TV reports said the suspects were of Middle Eastern nationalities. Neighbors interviewed by the BBC described them as quiet people who had lived in the neighborhood for a few weeks.
Two people arrested on the M6 highway in Northern England early yesterday were described as a man and a woman in their mid-20s. Police made the arrest after Saturday night's closure of the city's Liverpool John Lennon Airport, where they investigated a suspicious car.
By yesterday afternoon, both Glasgow and Liverpool airports were reopened under tight security. Similar security measures are in force in other airports nationwide.
At Glasgow airport, the burnt-out structure of the Jeep was removed from the shattered doorway of Terminal One and taken for forensic tests. Burned-out canisters of liquid gas were found inside the vehicle.
In central England, police were searching houses in Newcastle-Under-Lyme in Staffordshire. Neighbors told British reporters that the man arrested on the M6 highway lived in one of the houses and that he was a physician from Lebanon who worked at a local hospital.
Clarke, who traveled to Glasgow to help coordinate the investigation, called for public support yesterday and was upbeat about the "wider investigation."
"We are learning a great deal about the people who were involved in the attacks in Glasgow and the attempted attacks in central London," he said. "The links between the three attacks are becoming ever clearer."
The investigation has been propelled by intelligence recovered from a mobile phone that suspects tried to use as a remote triggering device in a car bomb left outside a London nightclub, officials said.
The Mercedes failed to explode when the suspects called the mobile phone rigged to propane- and gasoline-based bombs, officials said. That gave the police crucial leads, along with images from security cameras and evidence gathered at the Glasgow airport.
Investigators believe the suspects in London left two explosives-packed cars near a nightclub in a plan to set off a first explosion, draw emergency services and spectators to the scene and then set off the second one to heighten casualties and confusion, the official said.
The method of staggered multiple bombings is often used by insurgents in Iraq and also has been employed by Basque separatists in Spain.
Investigators believe the suspects arrested on the highway had direct links to the London plot, said sources close to the investigation. The propane cylinders found in the two cars in London and the Jeep used to ram the Glasgow airport were almost identical, sources said.
The Glasgow attack does not appear to have been well-planned, officials and analysts said.
"I am not sure how much thought went into that," the security official said.
Janet Stobart and Sebastian Rotella write for the Los Angeles Times.