Three senior judges dismissed an appeal brought by 24 claimants against a decision by a high court judge last December that the condition - dubbed "economy-class syndrome" - was not an accident under the terms of the 1929 Warsaw Convention.

Lord Phillips, the Master of the Rolls, sitting with Lord Justice Judge and Lord Justice Kay, announced at the beginning of their ruling that the appeals were "dismissed".

Solicitors for the claimants - who included survivors of DVT and relatives of those who died - described the decision as a "major blow". Ruth Christoffersen, whose daughter Emma died in 2000 after suffering DVT on a flight from Sydney, said: "I am saddened and disheartened at today's decision. Nothing can bring our daughter back, but the judges have shown compassion for the airlines only.

"They all have a responsibility to the general public to advise them of the dangers of flying and protect them from harm."

Solicitor Desmond Collins, of Collins Solicitors, commented: "This litigation has been lengthy and expensive for a lot of people. Today's ruling has been unhelpful on an uncertain point of law and provides no uniformity with other jurisdictions.

"New European legislation, anticipated shortly, will compensate financially passengers whose flights are delayed, yet victims of DVT fail to be recognised. For the sake of the law, the victims and their families, we are determined to take this to the House of Lords."

John Smith MP, who introduced his aviation health bill in the House of Commons yesterday, said: "This is a disappointing result and a setback for the general safety of the flying public. I urge both the House of Commons and the House of Lords to unite in bringing about justice as well as a change in the law to guarantee corporate responsibility."

The 18 airlines involved in the contested appeal include British Airways, Qantas, Airtours International Airways, Monarch Airlines Ltd, JMC Airways Ltd, Virgin Atlantic Airways, and Continental Airlines.

There were originally about 50 claimants in the group action, but the judges heard that the remainder did not have the funding to continue with "expensive" litigation.

DVT is a blood clot, usually in the leg, which develops when movement is restricted. It can be fatal if the clot reaches the lungs or brain. Airlines say there is no evidence of a specific link between flying and DVT.