Blood clot victim Emma Christoffersen: Family are calling for an inquiry

Several people who say they suffered so-called "economy class syndrome" are also suing major airlines and Australian aviation authorities.

The study will involve up to 10,000 medical and travel records held by government agencies to reveal the proportion of travellers who have developed blood clots during flights, Deputy Prime Minister John Anderson said.

'No link'

Recent research has been inconclusive about the dangers of long haul travel.

In October last year Dutch scientists assessed 788 patients and concluded there was no link between travel and the potentially fatal condition.

Airlines are being urged to put warnings on tickets

But a further study by at the University of Oslo found that 10% of the 100 patients studied developed clots after travelling.

And in March this year, World Health Organisation experts and airline representatives said there was likely to be a link between long-haul flights and blood clots.

Clots develop in blood vessels in the legs when circulation slows, usually because people stay still for long periods.

The condition is known as deep vein thrombosis (DVT). The clots can be fatal if they break off and are carried to the lungs, blocking the flow of blood.

Inquiry call

Preliminary results of the Australian study are expected in March next year.

Mr Anderson said: "Our health experts consider the study will provide an excellent basis for deciding what further research is required, and whether we need to take additional steps to reduce the risk of DVT."

Emma Christoffersen, 28, from Newport in Wales died last October, when she collapsed after a 20-hour flight from Australia.

Her family is calling for an inquiry, claiming that airlines have known about the condition for about 30 years, but did not warn customers about the risks of cramped seating.