SYDNEY -- Virgin tycoon Richard Branson on Wednesday said television viewers were as vulnerable to so-called "economy class syndrome" as airline passengers and vowed to defend a landmark lawsuit launched in Britain this week.

Branson's Virgin Atlantic is one of up to 30 airlines cited by 56 families claiming in the British courts that there is a causal link between deep vein thrombosis (DVT) -- the formation of a blood clot in an artery -- and air travel.

The case has the potential to affect millions of air passengers around the globe but Branson said it was not an issue for the airline industry.

"I don't regard it as a major issue because I think in travelling 50 million passengers we've only had one incident," AFP quoted Branson as telling reporters.

"I think that with 50 million people on the ground there'd be one or two incidents as well. "Obviously it's horrible that it happens but I actually don't believe that anybody's any more likely to have a problem than they are watching the television."

Branson said Virgin Atlantic advised passengers to move around during flights "as you would if you were at home, or in a train or in any other situation".

He said Virgin Atlantic would strongly defend the case but was unsure whether it would act individually or with other airlines.

DVT, also known as economy class syndrome, is believed to result from long hours of inactivity, particularly of the legs, such as during a long-haul flight.

Lawyer for the victims, Stuart Cakebread, said it could leave its victims crippled for life or dead.