The report said millions of pounds a year are spent abroad

The group said doubling the airport's capacity could lose the region �78m a year which holidaymakers spend abroad.

The figure is based on research by sustainable transport expert Professor John Whitelegg.

But Bristol Airport said it stands by government research which directly links economic wealth with its growth.

'Claw back'

Managing director Andrew Skipp said: "If we don't allow the airport to grow, they will use other airports for their business and leisure needs.

"A large amount of Bristol's growth will come from people currently flying from Heathrow and Gatwick, we will claw them back."

But the study said Britons spend much more abroad than visitors to the UK, regardless of where they fly from.

"Air travel and tourism acting in concert take resources out of the UK and the south west and as a result damage the economy," the report said.

Jeremy Birch, from Stop Bristol Airport Expansion, added: "All the airports are planning to double and triple, it's not taking people away from Heathrow, there will be more trips.

"The demand for air travel has been created by low air fares. It's an artificial situation. More and more people are flying out on cheap flights and not driving down to the south west and spending money there."