Of all the detail about the bomb plots over the weekend, the fact that the perpetrators seem to be linked by their medical training has caused the most consternation. How can a doctor want to kill, and an NHS doctor at that? How can anyone working in the National Health Service, that quintessentially British institution, not only not feel British, but actually hate Britain?

Even to ask the questions is to misunderstand to a degree what the National Health Service is: not, in fact, the essence of Britishness but to a large extent foreign. Nearly four in ten doctors registered to work in the UK (they are not necessarily all working here) qualified overseas, in 150 countries from as far afield as Ecuador and Ethiopia, Somalia and Singapore. By far the highest number are the 27,558 who qualified in India, but the list includes 6,634 who qualified in Pakistan, 2,581 in Egypt, 1,985 in Iraq, 819 in Bangladesh, 488 in Iran, 155 in Malaysia, 64 in Afghanistan and even 5 in Indonesia.

Among the nurses and midwives newly registered in 2005-06, a quarter were from outside the United Kingdom and the European Economic Area. We have nurses from India and Nigeria, the Philippines and Botswana, Pakistan and Ghana. (Meanwhile, UK-based nurses and midwives are fleeing overseas, mainly to Australia, the United States, New Zealand, Ireland and Canada.)

To assume that all these doctors and nurses are happy to be working in Britain is naive. Many will guiltily have left home countries that paid for their training and which need them far more than the NHS does. Male life expectancy in Ethiopia is 50, in Nigeria 47, in Botswana 42. In Pakistan it is 61, in Iraq 51; in the UK it is 77.

Many of the foreign medical staff will have intended to return home after a short period, but stayed: their families back home need the money they send them, or the standard of living here is just too attractive, or they have had children in Britain and seen what the UK can offer their kids by way of a better future. Guiltily, they turn their backs on the countrymen who need them. Even second-generation British doctors can find themselves pressured by their parents, or feel the pull themselves, to go back and help the country that is in their blood and needs them more.

In Iraq – and no, this is not an apologia for the bombers – doctors have been badly hit by the war: killed or forced to flee, or working with severe shortages of drugs and equipment amid overflowing casualties. Any Iraqi doctor working in the UK may have mixed feelings about what he is doing, helping the citizens of a country he might even blame for destroying his own. It must be hard sometimes for him to stay in Britain, but it’s harder to leave. I can just about begin to imagine the guilt an Iraqi doctor might feel at enjoying the relatively stress-free, healthy life of an NHS doctor in Britain while his fellow Iraqis back home struggle with a desperate shortage of medical staff.

There is no excuse for the actions, if they are proven, of the foreign doctors and medical students involved in the weekend’s terror plots. Nor, to a secular Western mind untrained in psychology, is there any causal link between dissatisfaction, guilt and religious fanaticism, let alone murder. But I am sure that a psychologist would have less trouble than I in joining the dots.

The enlargement of the NHS in the past ten years, and its success in cutting waiting lists, has been built on the backs of foreign labour. We have helped to bleed some of the poorest and sickest nations of the world of medical staff. Although the NHS has been banned since 2004 from hiring healthcare staff from countries where they are in short supply, only 140 of the 800 recruitment agencies that supply staff to the NHS have signed up to the code. And medical staff hired by the private sector, who subsequently transfer to the NHS, are not covered.

Nor need we pretend that many of us have been too concerned about it. We are more interested in how we are treated than who treats us; how fast we proceed up the queue, not how fairly.

The Department of Health fails even to collect figures that might be considered unpalatable, but the Conservative MP Peter Lilley winkled some out last month. He discovered from the Home Office that more than 5,500 nurses and more than 600 doctors from Africa were given UK work permits between January 2006 and May 2007. Since 2000, UK permits have been issued to more than 4,000 African doctors and 53,000 African nurses. That is, said Mr Lilley, one in eight of all the nurses on a continent where life expectancy is as low as 37. While the department claims that the NHS does not recruit from Africa, the agencies that supply the NHS do, and the Home Office issues them with work permits.

I read yesterday that, now we know about doctor-bombers, no longer should we fool ourselves that poverty is a precondition for radicalisation. But there are plenty of inequalities other than the purely financial. Look at some other figures that Mr Lilley has discovered: 1,500 African teachers came here between January 2006 and May 2007, and more than 500 Asian ones. We gained more than 10,000 nurses and 2,400 doctors from Asia in the same period. We take the professionals that these countries most need and use their skills to enrich the UK.

Nowhere can inequality be so devastatingly stark as in a well-resourced British hospital where a well-fed patient, preparing to have her varicose veins removed, complains to an Iraqi doctor whose medic brother was killed for treating bomb victims back home; or a Malawian nurse whose young child died of an easily preventable disease; or a Zambian whose life expectancy at home would be lower then the age of the woman in the hospital bed – where she complains to these people treating her that the food sucks or she hasn’t got enough pillows or painkillers.

No, murder is never excusable, and often impossible to understand. But resentment; even hatred; some burning anger for a fanatic to build on? Oh yes. Surely we can stretch ourselves to understand that.

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