Illustration by David Simonds

THE NHS is the closest thing the English have to a national religion, Nigel Lawson, a former Tory chancellor, once observed. Seldom has that tart comment seemed more apposite than in recent days, as both Gordon Brown and David Cameron leapt to the defence of the NHS following vitriolic criticism in America of Britain's “Orwellian” health service. Some of the charges against it are absurd, but does the tax-financed NHS deserve such worship this side of the Atlantic?

Comparing the performance of health systems is tricky. For one thing, people may attach different values to crucial features such as coverage, choice, equity and the quality of clinical care. For another, people's health reflects influences like lifestyles that have little to do with medical care. Cost must also be taken into account. The World Health Organisation attempted an evaluation in 2000, in which Britain came 18th out of 191 countries and America 37th, but the methods used to compile the ranking were heavily criticised and it has not repeated the exercise.

On the most basic metric of life expectancy at birth, Britain (79.1 years) outscores America (77.8). Longevity is admittedly a crude and indirect indicator of population health. Yet a similar story emerged from a study in 2006 that used direct measures to compare the health of middle-aged people: the Americans were sicker than the English.

Another line of inquiry is to investigate how health systems perform in tackling conditions that are treatable, comparing death-rates for such illnesses among the under-75s. Britain does not emerge well from one such ranking, compiled by Ellen Nolte and Martin McKee of the London School of Hygiene and Tropical Medicine. Their study, published in early 2008, placed Britain 16th among 19 advanced countries (France came first). But America came last.

On the other hand, Britain scores worse than America in five-year survival rates for cancer. High-tech diagnostic equipment is less abundant: in 2007 there were, for example, 25.9 MRI scanners per million Americans compared with 8.2 in Britain. Expensive new drugs generally become widely available sooner in America than in Britain. One reason is that in Britain they are subject to a cost-benefit assessment. Although this approach has been demonised in America it merely makes explicit the rationing in any medical system through the decisions of insurers and funders.

And then there's the question of overall cost. Even after a huge expansion of the NHS budget over the past decade, spending on health care in Britain amounted to 8.4% of GDP in 2007 compared with 16% in America, according to the OECD. Public spending on health care per person is actually higher in America (through Medicare, Medicaid and other government programmes).

Both health systems have their virtues and their faults. At its best, America offers extraordinarily good clinical care, but too many people lack insurance cover or fret about losing it. The NHS provides health care to all at a much lower total cost, but patients have less clout. Both countries are crying out for reforms to bring about better and cheaper care.