A new study of 100 passengers has revealed 10% developed clotting as a result of flying.
Blood clots in the legs can lead to deep vein thrombosis which kills dozens of air travellers each year as the clot works its way to the heart and lungs.
The condition has been dubbed "economy class" syndrome, as cramped seats, lack of mobility and dehydration suffered by economy passengers on long-haul flights make it difficult for blood in the legs to flow properly.
The report's author, John Scurr, said the study was specifically designed to trace blood clots caused by flying.
Ultrasound scanners
"We studied the patients before they went. It was really only because of the flying that there was a difference," he told Sky News.
He said it was unlikely that any other activity would have caused the blood clots.
The study used ultrasound scanners to detect the presence of clots in the blood stream.
Volunteers, aged 50 and over, were tested before and after their flights.
The report follows the death of bride-to-be Emma Christoffersen in October.
The 28-year-old fitness fanatic from Newport, South Wales, died from a blood clot brought on by sitting in a cramped seat for 20 hours of a 10,000-mile journey from Australia.
Pressure test
A Department of Health spokeswoman said the research would be examined with interest.
"There is a lot of conflicting information at the moment," she said.
"We are reviewing the situation and asking people who have been ill and believe it was due to flying to contact us.
"We need to make a proper assessment of the situation."
Similar findings elsewhere
The survey is expected to be published in The Lancet medical journal, which recently published details of similar research in Norway.
Researchers from Oslo put 20 healthy male volunteers in a "hypobaric chamber", where the air pressure was manipulated to simulate the pressure normally encountered within aircraft cabins.
The experiments also suggested the sudden change in air pressure experienced within the cabin may be partly to blame for the increased risk of blood clots.