Of the eight people arrested over the attempted car bombings in Glasgow and London, seven are doctors or medical students and one a lab technician, all with links to the NHS.
Doctors must be registered with the GMC to practise in the UK
Among them are three doctors who qualified in Jordan, India and Iraq.
The NHS has traditionally depended on overseas doctors to help keep the health service running.
The most recent figures show that almost 128,000 of the 277,000 doctors on the GMC register have been trained abroad.
Of these 1,985 are from Iraq and 184 from Jordan.
The skills gap has meant that, with the exception of consultants, doctors did not require a work permit until last year.
Ministers changed this only as the expansion in medical school places several years ago led to a boom in UK-trained doctors.
The Home Office is now in charge of issuing work permits and visas as it would for other professions.
Doctors coming from overseas are required to undergo several other NHS checks to ensure they are fit to practise.
Foreign doctors who have qualified outside the EU have to pass a series of linguistic and clinical tests before they can register with the General Medical Council (GMC), the profession's regulatory body.
The GMC then issues a limited registration but once the doctor has been working in the NHS for a little while they would be expected to apply for a full registration.
However, under European legislation, doctors who gain their qualifications in countries within the European Economic Area - EU countries plus Norway, Switzerland and Liechtenstein - have a right to registration in Britain and are exempt from the GMC's tests.
NHS trusts are also required to carry out checks on doctors they employ. These include checking for GMC registration, identification, passport credentials and criminal records.
Sian Thomas, deputy director of NHS Employers, which represents health trusts, said she wanted to reassure the public there were "thorough and robust checks" in place.
But these tested "their merits to do the job they do", rather than for political or extremist affiliations.
Ms Thomas said the NHS did not see it as its job to be checking for such connections and that she did not think the vetting process should be changed to do this.
"While doing all they can to prevent unsuitable people taking up employment in the NHS, employers also have a duty to look after the rights of their staff and this includes not discriminating against employees in any way on the grounds of their religion or belief."
There are also restrictions covering which countries the NHS can recruit from.
A code of practice bans the health service "actively recruiting" from countries facing a so-called brain-drain.
The list includes Iraq, although doctors from that country are still entitled to apply themselves for posts in the NHS.
However, if any doctor is charged in connection with the attempted car bombings, it may have a consequence for the medical profession.
Dr Abdula Shehu, a member of the Muslim Doctors Association and chairman of the Muslim Council of Britain's health committee, said he was worried about a possible backlash against Muslim doctors.
"To generalise for an event like this and think that Muslim doctors generally should have a different kind of treatment or perception in a negative way should not be the issue here."
Dr Edwin Borman, chairman of the British Medical Association's international committee, said if allegations were proven against doctors it would be a "betrayal" of society because of the oath they sign up to promising to do no harm.
But he added: "It must be remembered that the NHS has benefit from doctors [from abroad]."