British intelligence services also believe that the failed car bombings in London and Glasgow bear the fingerprints of al Qaeda in Iraq.
Intelligence sources tell CBS News that the people behind the attempts were directly recruited by Abu Hamza al-Muhajir, the present leader of the terror group's Iraq franchise.
Sources say that al-Muhajir recruited people for the plot between 2004 and 2005, while they were living in the Middle East, upon orders from then-al Qaeda in Iraq leader Abu Musab al-Zarqawi.
Al-Muhajir was told to recruit young men who could easily move into Western countries, assimilate and lay low until the time came to attack. Britain has a fast-track visa program for medical students which makes it easier for them to enter the country.
The belief that this small cell of militants was recruited purposely by a major terror organization for their specific qualifications differentiates the group from the cell of "homegrown" attackers who were behind the bloody July 7, 2005 attack that left 52 people dead on London's transport network.
All the suspects now being held are foreign doctors, or health workers who have worked in Britain, reports CBS News foreign correspondent Mark Phillips. For potential terrorists, it was a useful cover.
Not only was it frighteningly easy for the bombers to get into the country, getting the ingredients for their bombs was surprisingly easy as well. They just drove about five miles to their local home improvement store, where they could buy the gas cylinders for about $60 each.
Iraq's national security advisor has been warning American and British authorities that al Qaeda has been infiltrating operatives in Europe, reports CBS News foreign correspondent Sheila MacVicar. And he said that al Qaeda is changing its style, seeking the highly intelligent and well educated — just like the doctors involved in this terror plot.
Sources close to the investigation tell CBS News that two or three arrests were likely to be seen in Britain by the end of the week and that some of the arrests will be of British nationals.
There have been a number of security scares since the failed car bombings, the latest coming Tuesday afternoon with authorities evacuating Terminal 4 at London's Heathrow Airport for five hours.
"A suspect bag was identified shortly before midday in Terminal 4," said a statement released by the British Airports Authority.
"As an extra precaution, it was decided to perform secondary searches on all departing passengers at the aircraft gate," which necessitated the evacuation of the terminal, the statement added. Authorities "stood down" the security situation five hours later and reopened the terminal, according to a later statement from the BAA.
Tuesday morning London police briefly blocked traffic around Hammersmith Station, in west London (seen at left), due to a suspicious package. The situation was quickly resolved by a controlled explosion.
(Gareth Cattermole/Getty Images)
No explosives were found and morning rush hour traffic was soon allowed back through the area.
The eighth arrest confirmed as part of the bomb plot investigation was made Monday in Brisbane, Australia. The 27-year-old man is also a doctor who had been working in Liverpool, England until a few months ago, according to CBS News sources.
Britain's Sky News identified the man as Mohammed Haneef, and reported that was arrested at Brisbane's airport as he attempted to board a flight with a one-way ticket. Sky said officials had refused to confirm reports that Haneef was bound for India, via Kuala Lumpur, Malaysia.