The condition has been dubbed "economy class syndrome" because passengers sitting on long-haul flights without space to stretch out were considered as most at risk.

The New Zealand team examined a sample of 62 people admitted to hospital with blood clots, and found 34% had been sitting at their desk for long periods.

In comparison, 21% had recently travelled on a long-distance flight. However, the researchers accepted that many more people sit at their desk for long periods, than travel on long-haul flights.

Lead researcher Professor Richard Beasley said some office workers who developed clots sat at their screens for 14 hours a day.

He said: "Some of them were going three to four hours at a time without getting up."

Anna