Fifty-six people are fighting a landmark legal case against 28 airlines for failing to warn them or their relatives about the risk of DVT, also known as economy class syndrome.

Counsel Stuart Cakebread told the court in London there was a "profound" impact of flying for long hours in cramped conditions.

The three-day hearing began on Tuesday and will consider whether DVT can be classed as an accident under the terms of the 70-year-old Warsaw Convention.

They or their deceased relatives have been injured or killed as a result of flying

Stuart Cakebread Counsel

This could lead to airlines having to pay out significant damages to victims or their families.

The court heard the counsel's intention to focus on the issues of international law, human rights and international treaties.

Mr Cakebread told Mr Justice Nelson and the court: "But, we must not lose sight of the fact that the outcome of this action is of the most profound personal importance to the 56 claimants.

"All say that they or their deceased relatives have been injured or killed as a result of flying in the defendants' aircraft.

Emma Christoffersen from south Wales died after a long-haul flight

"All the victims suffered their injury whilst in the care of the defendant airlines, the symptoms appearing either at the time or shortly afterwards."

Mr Cakebread said there was "a causal link between air travel and DVT".

He described DVT as a condition where a small blood clot forms in the deep veins, particularly in the legs, and complications in other organs can lead to death.

He said the claimants suffered because of "acts and omissions" by the airlines, including seating too close together and a failure to warn passengers of the dangers.

'No link to flying'

Before the hearing, lawyer Des Collins, who is representing the claimants, said he believed these claims were just the tip of the iceberg.

He condemned the airlines for an "appalling silence" about the alleged risk.

The airlines are expected to argue they are protected under the 70-year-old convention from paying compensation for medical problems classed as a passenger reaction to the normal operation of an aircraft.

Six relatives are among the claimants

They have denied liability and say advice given by the government and the World Health Organisation suggests no specific link between flying and DVT.

The advice they offer passengers during flights is a reaction to their concerns and media reports, the airlines claim.

Sarrol Khan, director of the Aviation Health Institute, says he doubts the claims will succeed because of the strict wording of the Warsaw Convention which governs such cases.

The 56 claims relate to passenger DVT-related deaths and injuries.

Among those bringing claims is Timothy Stuart, of Llanmartin, Newport, south Wales, on behalf of his former fiancee, Emma Christoffersen.

The 28-year-old died two years ago after developing a blood clot on a 20-hour flight from Australia to London.

Tips to lower the risk of developing DVT include walking around the aircraft during a flight and wearing tight stockings.

Have you experienced any of the issues raised in this story? Send us your views using the form below.

I am just thankful every day that I am still alive

Lisa Brown, UK

I am 22 years old, and in May of this year I developed a very large DVT in my thigh. I am young, fit, slim, do not smoke or drink - I had also not been on an flight for over a year. Although seriously ill, it never crossed my mind to blame anyone. I am just thankful every day that I am still alive and on the way to making a full recovery.

I am not saying the airlines should or should not be held responsible for these cases. It is worth remembering that those that are still here to fight this case have already won a huge battle - they are still alive. My condolences got out to those who have lost a loved one, but what joy will this court battle bring them?
Lisa Brown, UK

As long as people want cheaper air travel, the airlines will continue to cram more passengers into aircraft. My sister was a flight attendant with a charter airline. When people complained about the lack of room, she used to tell them to go and pay double the amount to fly with BA, and get more room.
Tracey, UK

After flying from Toronto to Manchester on a six hour flight I developed a limp in my right leg, the pain got worse over a couple of days so my husband made me go to the hospital. I did not think that six hours was long enough to develop DVT. And I was moving my legs during the flight. But I was wrong! It was a DVT.
Joanne Thibodeau, UK

I've seen cabin crew becoming openly irritated by passengers walking up and down the aisles

Judy, UK

It's extremely difficult to follow the guidelines of walking about the cabin or exercising your legs when you are in a cramped middle section seat surrounded by other passengers and their luggage. I've experienced cabin crew becoming openly irritated by passengers walking up and down the aisles. Perhaps designated time intervals could be announced for passengers to adequately stretch their legs without interfering with meal or drinks service and to avoid inconveniencing fellow passengers who might be sleeping.
Judy, UK

At 81 years of age, I travel between the island of Mallorca and LA at least once every year and the airlines have been giving advice to move around and/or do exercises in one's seat for at least the 16 years that I have been making the journey. So they cannot be held responsible.
Betsy Zill Phillips, USA/Spain

My wife who is a little over five foot has experienced severe discomfort on some cheaper flights, and could not even bring her knees together on one, despite her small stature. It is impossible to assume the correct position for an emergency landing if the seat in front is too close.
RH Rawlinson, UK