Women in particular need to be made aware that the pill, pregnancy and hormone replacement therapy all increase the risk their developing DVT

Brent Escott, Club Direct

He said passengers must be made aware of the specific causes of the condition, and it was the responsibility of the air industry to arm them with the relevant information.

"We want all airlines to take some responsibility for warning people about the risk of getting DVT on flights, particularly when higher-risk groups of people are concerned," he said.

"It's impossible to prevent all people getting DVT, but a few words from the airline or travel agent about how to reduce the risk will save many lives.

"Women in particular need to be made aware that the pill, pregnancy and hormone replacement therapy all increase the risk their developing DVT."

DVT deaths

More than 40 long-haul airline passengers have died from DVT clots.

They include Emma Christoffersen, from Newport, Susan Mavir-Ross, from Llay in Wrexham, Thomas Lamb, from Cardiff, and John Thomas from Cowbridge, south Wales.

Solicitors representing nearly 300 claimants went to the High Court in London in January to launch legal proceedings against 30 major airlines.

Medical research has shown that clots develop in blood vessels deep in the legs when circulation slows - when people remain seated for long periods, for example.

Emma Christoffersen died after a long-haul flight from Australia

The clots can prove fatal if they break off and are carried to the lungs, blocking the flow of blood.

Several medical reports have claimed a link between DVT and air travel, although it is yet to be proved.

British Airways has joined Birmingham University Medical School in a new research project aimed at examining awareness of DVT among regular air travellers.

BA is currently involved with the World Health Organisation in the development of a broad research programme that is looking at all aspects of DVT and air travel.