June Kelly: "The air industry seem to be taking this issue seriously"

Doctors want to discover if there really is a condition dubbed 'economy class syndrome'.

Mr John Scurr, a consultant vascular surgeon from London's Middlesex Hospital, is undertaking research into the possible link.

He will study issues such as leg room, cabin pressure and oxygen concentration. He believes thousands of people a year in the UK are affected by long haul flights.

John Scurr has launched the study

"We hear figures of 30,000 patients affected a year being bandied about. I think it is probably greater than that.

"A lot of passengers who get off aeroplanes will not have any signs for symptoms for a long time. The signs and symptoms develop many years later."

British Airways is also undertaking research in the area.

Legal case

Val Clarke, 58, from Gateshead, is suing Northwest Airlines, an American carrier, after she developed a clot following a trip from Minneapolis to Amsterdam.

Val Clarke explains her case

The clot was so bad that her leg had to be amputated.

The airline is defending the law suit, saying there is no evidence it was the flight that caused her problems.

Mrs Clarke said: "I can't walk too far, I can't sit too long. It has just totally wrecked my life, I am devastated."

Val Clarke had a leg amputated

The British Heart Foundation advises passengers on a flight of more than two hours to walk about at regular intervals to diminish the risk of a blood clot in the legs.

It also advises passengers to drink plenty of water and avoid excessive amounts of alcohol.

In a statement the Foundation also says: "If you have recently undergone surgery or have suffered from deep vein thrombosis, your doctor may suggest that support stockings are of benefit for long-haul flights.

"If you have painful and swollen calves after a flight, it would be advisable to see your doctor."

A spokesman for the Civil Aviation Authority said he was aware that long distance flights had been linked to blood clots.