New research – which looked at the experiences of millions of air travellers – found that the risk was no higher than 0.05 per cent, as it affects only five people out of every 10,000 passengers. The risk doubles among people who are seriously overweight or who have vascular health problems.

The only group at risk are people who wear a cast or splint, and who can move their legs only slightly.

(Source: German Institute for Quality and Efficiency in Health Care).