Citing sources in the intelligence services, CBS reported investigators say the attempts have al-Qaida's fingerprints. They believe Abu Musab al-Zarqawi, killed last year in a U.S. air strike, ordered Abu Hamza al-Muhajir in 2004 to recruit potential sleeper agents.
Eight people have been arrested since Saturday, when two men attempted to explode a car bomb at the main entrance to Glasgow Airport. Six of those detained have been doctors.
"There is concern they used a trusted profession, recently arrived to the U.K., that's a new mode of operation," Paul Kurtz, an expert on terrorism, told CBS.
The London Transport bombings in July 2005 were carried out by young men who had been born or spent most of their lives in Britain and become radicals in Muslim neighborhoods there. But the new suspects were living in the Middle East until recently, and intelligence agents say they were recruited because they could easily gain admission to western countries.
Notable deaths of 2014 [PHOTOS]