There can be few doctors who haven’t had at least one patient ask them about the value of health screening tests using computed tomography in the past few months. Look up momentarily from the pavement or your seat on public transport and it is highly likely you will catch a glimpse of an advertising hoarding promoting state of the art diagnostic machinery for an all over health check.

“Beat your silent killers” with scans tailored to your individual needs, say the websites of the clinics offering screening services. Some clinics even offer a reduction for loyalty, with repeat scans at a discount. Keep reading and the stories of early diagnoses that would otherwise have gone unnoticed can trigger worrying thoughts about what disease you could be harbouring—and make even long suffering NHS stalwarts reach for a credit card.

The clinics offer an array of preventive medical examinations. As well as full body scans there are scans for particular parts of the body—the heart, lungs, and abdomen are especially targeted because of their susceptibility to symptomless diseases that can kill suddenly. Comprehensive tests may also be needed, say the clinic websites. Ask for it and you can have it—computed tomography, magnetic resonance imaging, positron emission tomography, scans, radiography, ultrasonography, bone densitometry, spirometry, blood tests, urine tests, faeces inspections, electrocardiography, and echocardiography.

Although there are no official figures, anecdotal reports from general practitioners and hospital doctors suggest that many people find the adverts, the case histories, and word of mouth accounts of scanning experiences alluring. One company, Capio healthcare, which boasts a fleet of mobile scanners, says …