Emma Christofferson: DVT victim

The study comes a year after DVT hit the headlines with the death of 28-year-old Emma Christofferson from Newport, south Wales, who died within minutes of leaving a 20-hour flight after a holiday in Australia.

Three other people from Wales are believed to have died from the condition in the last year.

Susan Mavir-Ross, 42, from Llay near Wrexham, Thomas Lamb, 68, from Cardiff, and John Thomas, 30, from Cowbridge, Cardiff, all died after long flights.

DVT, also known as 'economy class syndrome' can cause death if blood clots that develop in a deep vein, often in the legs, break away and block the lungs.

The report published on Tuesday - part-funded by the UK's Civil Aviation Authority (CAA) - looked more at changes in the average weight and height of passengers in the past few decades than the highly-publicised fears over so-called "traveller's thrombosis".

It said that an increase of two inches in the minimum gap between backrests was needed for people to escape easily in the event of an emergency.

It also called for a minimum standard for the legroom given to passengers, and for seat cushions to be widened.

However, the report said that in theory, redesign of aircraft seats could reduce the risks of DVT - and that any new seat designs should be tested to see how they affected crucial blood flow in the lower legs.

John Smith MP has campaigned for action to combat suspected flight-induced DVT and has said: "We still want to know what the full extent of this problem is.

"We don't know if a handful of people have died from this condition or thousands."

'At risk'

According to the medical journal The Lancet, one in 10 of long-haul passengers is at risk from the condition.

Last week's British Medical Journal showed that around 10 people die from a blood clot in the lungs each year within minutes of arriving at Heathrow airport.

Passengers are recommended to take aspirin, which will help to thin the blood, to exercise during the flights and to drink fluids but to avoid alcohol.