By Daniel Morrissey LONDON, Jan 31 (Reuters) - A British court cleared the way on Thursday for a class action suit against up to 30 airlines worldwide over blood clots suffered by passengers on long-haul flights, dubbed "economy class syndrome". The airline industry, already in a financial tailspin from the global economic slowdown and the September 11 attacks in the United States, could face millions of dollars in claims from hundreds of people around the world. "We are delighted that the court has put in place the machinery to resolve this issue efficiently and effectively," said Des Collins, senior partner of the law firm representing the claimants. Claimants argue that a combination of cramped flying conditions and long hours in the air give rise to the condition, formally known as deep vein thrombosis (DVT). World airlines have said there is no definite proof linking DVT to air travel, but some have agreed to help a World Health Organisation (WHO) study into whether a link exists. The death of a 28-year-old woman after a flight from Australia to Britain in 2000 raised awareness of DVT and a number of incidents since have kept the issue in the headlines. In July last year, Australian law firm Gordon & Slater launched suits against three international airlines -- KLM Royal Dutch Airlines, British Airways and Qantas Airways -- and Australia's air authority CASA. At Thursday's hearing in London, lawyers representing both sides effectively agreed on a draft order to open the class action at England's High Court in London. "The sooner we get this action properly constituted within the framework of a group litigation order the better," said Master Turner, a senior high court official. The court will now seek approval of the draft order from the Lord Chief Justice of England before the legal battle begins later this year. Lyn Walcott of Essex, whose husband died after a flight to Barbados in October 2000, will be first claim in the class action to be served by February 7, said Collins's lawyer Stuart Cakebread, adding that the number of claims was approaching 300. The airlines will turn to the 1929 Warsaw Convention on air travel. The convention states that a carrier is only liable for damage to a passenger in an accident sustained while a passenger is aboard the aircraft or in the course of getting on or off the aircraft. Robert Lawson, a lawyer for some of the airlines, told the court on Thursday the "only true group issue" at the moment was whether DVT amounted to an accident under the convention. But Colin Hall, the managing director of aviation analysts Avmark International, said that several courts in the United States had overruled the convention on other issues. "The Warsaw Convention is not a protection of all airlines' legal liabilities. It helps but it's not a coverall," Hall said.