British Home Secretary, Jaqui Smith, said the decision to lower the threat from “critical” to “severe” had come after the authorities concluded that there was “no intelligence to suggest that an attack is expected imminently.” But in a statement, she said, “there remains a serious and real threat against the United Kingdom, and I would ask again that the public remain vigilant.”

While the lowering of the threat level may soothe nerves here, people are shaken by the disclosure that the suspects hatched their plot while working in Britain under the umbrella of the National Health Service.

Britain will conduct a thorough review of its policies for screening foreign doctors who want to practice here, Prime Minister Gordon Brown announced Wednesday. Brown, speaking in Parliament in his first appearance at weekly Prime Minister’s Questions, also said the government would also expand its worldwide watch list of potential terrorists.

“It is vitally important the message is sent out to the rest of the world that we will stand strong, steadfast, and united in the face of terror,” said Brown, who faced challenging questions from the Conservative opposition about his government’s treatment of radical Islamic groups.

Five days after a failed attempt to blow up cars in London and at Glasgow Airport, the police are confident that all the main suspects in the case have been rounded up, a law enforcement official said, speaking on condition of anonymity.

Seven of the suspects, all men, are physicians, according to the official, while the lone woman, the wife of one suspect, is a laboratory technician.

Attention is now turning to unraveling the links within the circle of doctors to determine how this network was organized.

Investigators searched two houses in Liverpool, where Shabeel Ahmed, one of the doctors allegedly connected to the plot, is believed to have been living.

Police officers in forensic suits carried out several bags of evidence, containing computer hard drives and documents.

Investigators were “at the very early stages” of trying to find out where the alleged conspirators came from, said a British official, who spoke on condition of anonymity, citing government rules.

“There are various overseas connections,” the official said, adding, “It’s possible there may be an interesting Iraqi angle.”

The possibility of links with Al Qaeda leaders in Iraq moved to the forefront after a claim made by an Anglican priest living in Iraq that he had been warned about attacks in Britain and the United States.

The priest, Canon Andrew White, said that, at a gathering of Iraqi religious leaders in Amman on April 18, one of the visiting leaders told him “those who cure you will kill you.”

He did not pay much attention to the language, White said in a telephone interview, and did not mention it to British officials when he told them about the meeting. However, when he saw that these attacks were apparently the work of doctors, he recalled what the man had said.

“He was a very bad man,” White said, “and I was told afterward that he was closely connected to Al Qaeda, but I don’t know definitely that he was connected to Al Qaeda.” He declined to identify the man by name but said he was a religious leader from Anbar Province.

'Those who cure you are going to kill you'

British cleric Canon Andrew White says an Al-Qaeda leader who met him in Amman on April 18 made a cryptic warning: "Those who cure you are going to kill you."

These are the doctors the British police now say are linked to the failed bombing plots in Glasgow and London

Khalid Ahmed Lebanon: Staff at Glasgow's Royal Alexandra Hospital identified this doctor as driver of the Jeep that was crashed into Glasgow airport

Bilal Talal Abdul Samad Abdulla (27) Iraq: Passenger in Jeep. Trained as physician in Baghdad. Diabetes specialist at Royal Alexandra Hospital

Mohammed Jamil Abdelqader Asha (26) Jordan: Of Palestinian descent,this Jordanian doctor worked at North Staffordshire Hospital

Marwa Asha (27) Jordan: Asha's wife, identified by British media as a medical assistant

Mohammed Haneef (27) India: Physician employed by Gold Coast Hospital in Australia's Queensland state. Held at Brisbane airport as he tried to board a flight. Worked earlier at Halton Hospital in Runcorn, England. Studied in Bangalore

Sabeel Ahmed (26) India: Held in Liverpool, worked at Halton Hospital. Also from Bangalore

Unidentified men (25 & 28): Said to be of Middle East origin. Staff identified them as a junior doctor and a medical student.

• Mohammed Asif Ali India: Detained with Haneef in Australia, was released without any charge

We'll expand background checks that are done where there are highly skilled migrant workers coming into this country
Britain's Prime Minister Gordon Brown in parliament