An airline today promised hugely overweight passengers who buy a second seat would get a refund if the flight was not full.

Air France already offered fat passengers the option of buying an adjoining seat at a discount.

Today it said they would be fully reimbursed for the second fare in 90% of cases.

A company spokesman said the obese who do not reserve a second seat may not be allowed to board, at the captain's discretion and if there is not an unoccupied adjoining seat.

"It's a question of security," a company spokesman said.

Three years ago Air France was sued by a 25 stone passenger it made buy a second seat for a full New Delhi-Paris flight. Air France was ordered to pay £8,000 damages and to reimburse the cost of the second seat.

Other airlines with similar policies on obese passengers include Southwest, JetBlue and American Airlines.