Cars were banned from approaching British airport terminals as unprecedented security measures were enforced yesterday to combat a suspected Al Qaeda bombing campaign. The terrorist threat level was at “critical” — its highest level — after two car bombs were found in London and a third, potentially devastating, attack was narrowly averted at Glasgow airport.

It has forced police and the government to take the draconian step of closing off all forecourts at airports. Passengers cannot be picked up or dropped off and must instead be directed to outlying car parks and bussed in.

Last night five people were in custody as it emerged that:

• The same two men may have been responsible for the Glasgow and the London bomb attempts;

• Police were on the trail of the suspected bombers before the airport attack and narrowly missed tracking them down;

• A doctor and a woman are in custody;

• Police are still hunting at least one suspect;

• Experts said the attack on Glasgow airport aimed to kill and maim hundreds in a massive fireball;

Prime Minister Brown raised the prospect of detaining suspects without charge for more than 28 days and allowing the use of phone-tap evidence in court.

Anti-terrorism police are confident they have the key terrorists involved in custody — one of them suffering from 90% burns after smashing a Jeep, packed with gasoline and gas canisters, into the terminal at Glasgow. But they are still searching for at least one more member of what is believed to be an Al Qaeda cell intent on launching attacks across the country.

Officers raided the house of Dr. Mohammed Asha, in Chesterton at around 10 p.m. on Saturday night. Neighbors said he was a Lebanese doctor working at the North Staffordshire Hospital and lived there with his wife and baby boy. Dr. Asha, 26, and a woman of 27 were arrested as police cornered them on the M6 freeway near Sandbach.

In Liverpool, people living near houses raided by police said they believed the occupants were medical students. They said two young Asian men had moved into the house, off Penny Lane, made famous by the Beatles song, a few months ago.

Declan Murphy, 22, a sports development student, said: “We always thought the two Asian men who lived there were student doctors — I once saw one of them with a stethoscope round his neck.” It is thought the house, which was raided by police at midnight, was empty and a man, age 26, was arrested a short time later at Lime Street railway station, Liverpool. The second raid in Liverpool was at Hatherley Street, where four Asian men in their 20s lived. There were no arrests. Neighbors said the four were from Pakistan and Yemen, and had lived in the property for only a few months. They attended Al-Rahma Mosque at the end of the street.

At Houston, near Glasgow, police said two other men, who are now in custody, are believed to have rented a semi-detached house and had only lived in Scotland for three months.

Assistant Chief Constable John Neilson said: “The people we have in custody came to Scotland a short while ago to seek work. I’m sure the community in Glasgow in particular will be reassured. These are not your young people.”

The police appeared to have been hot on the trail of the two men before they attempted their attack. The director of an agency that rented out the Houston property said he returned home around 10 minutes before the attacks in the airport to find a note from Strathclyde Police asking him to get in touch about two of his tenants.

Mr. Brown said yesterday 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.” He said it was “clear” the attacks in London and Glasgow were perpetrated by people who were associated with Al Qaeda and pledged, “Everything is being done in our power … to protect people’s lives.”