July 2 (Bloomberg) -- U.K. police have arrested an eighth person in connection with an attack on Glasgow International Airport and two attempted car bombings in London.

A man has been detained abroad by local authorities on behalf of the Metropolitan Police Service and is being held in custody, the Met said in an e-mailed statement, without disclosing in which country the man has been detained.

Earlier, police in Scotland arrested two more suspects in connection with the attempted bombings. Seven men and one woman are now in custody.

The two men arrested earlier, age 25 and 28, aren't believed to be Scottish, police said today in an e-mailed statement. They were detained late yesterday in the Paisley area, southwest of Glasgow, under anti-terrorism laws, police said without giving further details.

Prime Minister Gordon Brown's government stepped up security nationwide in response to the incidents June 30 in Glasgow and June 29 in London. Controls were tightened at airports, cars were checked and more police were patrolling crowded public areas. The Home Office raised its terrorist threat level to ``critical,'' the highest, meaning an attack is expected imminently.

Two men were arrested at Glasgow airport after their Jeep Cherokee, filled with flammable material, rammed into a terminal entrance and caught fire on impact. One was hospitalized for burns. Police arrested two more people, a 26-year-old man and 27- year-old woman, on the M6 highway in northwest England that evening, and a fifth, a 26-year-old man, in Liverpool yesterday.

Nationalities

The nationalities of the first five suspects aren't ``certain,'' Home Secretary Jacqui Smith said when asked on Sky News whether the attackers were foreign or British. She said the ``public needs to be vigilant about potential threats'' of more incidents and added that Britain shouldn't be intimidated by the attacks. Searches have been carried out in at least 19 locations, Smith told the House of Commons.

The Guardian newspaper, citing unidentified counterterrorism officers, said today that an al-Qaeda-linked cell of eight people was behind the attempted bombings. Police said today that at least one more suspect is being sought.

``It is clear that we are dealing in general terms with people who are associated with al-Qaeda in a number of incidents that have happened across the world,'' Brown said in an interview yesterday. ``We're dealing with a long-term threat. It's not going to go away in the next few weeks or months.''

Security

A judge gave police until July 7 to question three of the suspects who are being held at London's high-security Paddington Green police station. They are the man and woman arrested on the M6 and the man arrested in Liverpool, police said today in an e- mailed statement. Police can seek extensions of their detention, to a maximum of 28 days from the time of arrest.

U.K. government bonds, or gilts, gained today, pushing 10- year yields to near a three-week low. Analysts expect the pound to hold above $2 before the July 5 interest-rate decision by the Bank of England. It last traded at 2.0098, from 2.0088 at the close Friday. The benchmark FTSE 100 Index fell 20.70 to 6587.20 at 2:45 p.m.

Two of those arrested are doctors, including the man arrested on the M6, who received his medical training in Jordan, Sky reported. Photographs taken by passing motorists showed the woman he was with wearing a Muslim veil and dress. Police said the man lived in a house in Newcastle-under-Lyme, Staffordshire, which they were searching. The search of a second home in the town began today, Sky reported.

Sealed Off

Police also sealed off a building that provides temporary accommodation for doctors at the Royal Alexandra Hospital in Paisley, where the suspect burned at the airport was taken, and searched the offices of a doctor at University Hospital in North Staffordshire, north of Birmingham, Sky News reported. A bomb- disposal unit arrived at the Scottish hospital for a possible controlled explosion of a vehicle, Sky reported. A car was blown up at the Royal Alexandra Hospital yesterday by bomb experts. Police subsequently carried out a controlled explosion at the hospital, Sky said.

Police said they also had searched a suspect's rented house in the village of Houston, near Glasgow airport. The tenant had been seen wearing a stethoscope and was a doctor or medical student at the Royal Alexandra Hospital, Daniel Gardiner, director of the agency that rented the property to him, said today in a telephone interview.

Houston Suspect

Police were hunting for the Houston suspect before the airport attack, Gardiner said, suggesting they had intelligence about him. Officers left a card at the door of his agency while the office was briefly closed, asking staff to call police, Gardiner said. The card was found only 10 minutes before the attack, Gardiner said.

Police contacted the rental agency after records of phone use by a suspect in the London incidents showed calls from the Scottish business, Gardiner said.

``The real question is, is it part of a plan that is being directed by someone?'' said David Bentley, an analyst in terrorism law at London-based policy research group Chatham House. ``London today, Glasgow tomorrow, then maybe Birmingham or Manchester?''

The Glasgow attack came as police were conducting one of their biggest manhunts after dismantling two car bombs made from gas canisters, gasoline and nails left in the heart of London's West End shopping and theater district three days ago.

Fast-Moving

``The links between the three attacks are becoming ever clearer,'' Peter Clarke, the U.K.'s chief anti-terrorism officer, said at a televised news conference yesterday. ``The investigation is extremely fast-moving. New information is coming to light hour by hour.''

The incidents prompted the biggest terrorism alert in the U.K. since authorities foiled an Islamist plot in August 2006 to blow up aircraft flying from Heathrow airport to the U.S. Terrorists killed 52 people in London on July 7, 2005, in suicide bombings on the subway and a bus.

In London, police were examining images from security cameras to try to establish the cars' routes into the center of the city. They found the first bomb in a Mercedes parked outside a packed nightclub in Haymarket, close to Piccadilly Circus, at 1:30 a.m. on June 29. The second device, in a Mercedes parked between Haymarket and Trafalgar Square, was found hours after it was towed to a garage on Park Lane for being parked illegally.

Airport

Glasgow airport, which was closed to all flights June 30, resumed operations yesterday. The airport, operated by BAA Ltd., is 8 miles (13 kilometers) west of the city center and is the busiest of Scotland's three main airports.

London's Heathrow airport, Europe's busiest, shut traffic lanes closest to terminal buildings and urged travelers to arrive on public transportation.

Essex police arrested a man at Stansted Airport this evening after an unattended bag was discovered outside the terminal building at 6:50 p.m. Police said in a statement that a man was arrested when he returned to the bag, and that officers had ``some concerns'' about the contents of the bag, but that the airport is operating as normal.

Dropping off and picking up in front of BAA airports is ``severely restricted,'' the company said in an e-mailed statement. BAA, owned by Grupo Ferrovial SA of Spain, operates Heathrow, Gatwick and five other U.K. airports.

Security Increased

Commuters in London today will notice increased security at rail stations and on the street, police said. Vehicles approaching main rail stations, and their passengers, will be subject to random searches for the foreseeable future, a British Transport Police spokesman said.

At the Wimbledon tennis championships in southwest London, concrete blocks are being use to protect entry and exit points and the organizers urged visitors to use public transportation rather than private cars.

``We urge everyone coming to the event to allow more time for their journey,'' said Ian Ritchie, chief executive of the All England Club said on the club's Web site. ``Safety and security is of paramount importance to us.''

To contact the reporter on this story: Nick Allen in London at nallen14@bloomberg.net.

Last Updated: July 2, 2007 18:00 EDT