These days, even the most defiant smoker is unlikely to be ignorant of the health risks associated with a 40-a-day habit. But what if you could have an annual Cat scan of your lungs for cancer? To catch out nodules twisting into shadows of malignant cells. If that scan was clear, would you stop smoking? Or would you light up outside the hospital and take your chances for another year?

In a study published in JAMA Internal Medicine this week, almost half of smokers (49% of 35 participants) who received the all-clear for lung cancer said screening lowered their motivation to give up. Dr Steven B Zeliadt, its lead author, stated: “If we want to save lives from smoking, we should take all this money being spent on screening and double down on smoking cessation efforts.” These things are hardly binary: it does not have to be either screening or cessation. Nonetheless, screening was found in one study to reduce lung cancer deaths by 20% – prompting a US screening programme.

Conversely, screening can provide false reassurance, with a temptation to ignore other risks: heart attacks, emphysema, stroke, diabetes, peripheral vascular disease and a protean range of cancers. Meanwhile, false positives can lead to potentially needless invasive investigations and treatments.

Increasingly, there is an appreciation that we need to discuss screening, with its inherent caveats as well as merits. Patients in the study wished for screening and smoking cessation to be equally beneficial. Easier to choose an annual scan than to stop smoking.

A university lecturer once said to me: when a patient tells you how many cigarettes they smoke, double it. When they tell you how many pints they drink, treble it. When they tell you how many times a week they have sex, divide by four. He might have had a point.