Thanks to the mass of evidence available to the police from the failed bombings and to forthcoming information from those who have been arrested, the investigation into the two linked terror plots is proceeding apace—and spreading well beyond Britain. The latest arrest was at Brisbane Airport in Australia. The man being held has been named by the Queensland Medical Board as Mohammed Haneef, 27, an Indian doctor who had been working in the emergency department at the Gold Coast Hospital in Southport, in the eastern Australian state of Queensland, since leaving a job in Liverpool, England, last year.

Haneef joins a cast of detainees that includes two other doctors whose names have surfaced. Last Saturday evening Mohammed Asha, 26, was arrested by antiterror police in unmarked cars as he drove along the M6 motorway in Cheshire, England, apparently with his wife and 2-year-old son. Asha is a Jordanian of Palestinian descent who worked as a neurologist at the University of North Staffordshire, Stoke-on-Trent, England. His father, Jameel, says the police must be mistaken: “I know my son and he’s not into these things.”

Multiple news accounts have identified one of the two suspects in the Jeep attack at Glasgow Airport as Bilal Talal Samad Abdulla, an Iraqi who reportedly qualified as a doctor in Baghdad in 2004. He worked at the Royal Alexandra Hospital in the Glasgow suburb of Paisley. The other men who have been arrested have not been named, but they have been widely identified as either doctors or medical students, giving rise to widespread speculation about a “doctors’ plot” against Britain. The threat level remains at the highest level, “critical,” which means the authorities believe another attack is imminent.

In that sense, Britain was coming to terms with a new kind of threat to national security. The country’s security services have long been concerned about Al Qaeda recruits coming into the country from the Middle East and South Asia, but the general population has focused its attention on the London mass transit bombings on July 7, 2005, in which 56 people, including four suicide bombers, died. Three of those bombers were Britishborn. The fourth was a Jamaica-born British citizen who came to the U.K. when he was a child. So the idea that plotters might have slipped into Britain from abroad—possibly even as a sleeper cell of some kind - adds a new dimension to public concern.

None of those arrested has been charged with a crime. But that has not prevented a lot of speculation as to how and when they came to Britain. According to the British General Medical Council, Bilal Abdulla received a “limited registration to work” visa in the U.K. on Aug. 5, 2006, and Mohammed Asha received his on March 31, 2005. Like thousands of other non-British doctors, they may have taken advantage of a temporary relaxation of regulations that was designed to make it easier for the NHS—with 1.3 million employees, one of the largest employers in the world—to hire doctors.

Since 1997, when the Labour Party came to power, the governments of Tony Blair and Gordon Brown have poured billions of pounds into the NHS to improve services. The NHS scurried to fill doctors’ slots with overseas practitioners. According to the most recently available statistics, more than 89,000 of the 240,000-plus doctors working for the NHS were qualified in foreign countries. That includes more than 6,000 from the greater Middle East. The largest single cohort came from India—more than 27,000.

Haneef, the Indian doctor arrested at Brisbane International Airport yesterday evening, was apparently detained at the request of British police. Philip Ruddock, the Australian attorney general, said that Haneef had been trying to board a plane to leave the country with a one-way ticket. A second doctor from the hospital where Haneef worked was also reportedly being questioned, although he has not been arrested. According to reports in Australia, he, too, is not an Australian citizen. Haneef qualified to practice medicine in 2002 at the Rajiv Gandhi University of Health Sciences in Bangalore, but, according to reports, he then moved to Britain to take up a job at a hospital in Liverpool.

Police hunting down the team behind the Glasgow and London attempts arrested an unidentified man in Liverpool on Sunday, after raiding two local addresses. It is not known if this arrest is connected to that of Haneef. Last year Haneef responded to an advertisement in the British Medical Journal to work in Queensland. He was interviewed in June, and arrived to take up his post in September, moving with his wife into the Gold Coast apartment building near the hospital, according to reports in Australia. He was employed under Australia’s temporary skilled worker scheme. Peter Beattie, the Queensland premier, said: “According to the hospital, he has been a good employee… The doctor is regarded by the hospital in many senses as a model citizen, with excellent references and so on.”