An investigation by Which? has found that members of airline frequent flyer schemes have to make as many as 20 return journeys on the same airline before they are entitled to a free ticket.
Passengers can rack up thousands of points through flight purchases but when they convert the points into flights, they are often left disappointed. Even when they have enough points, there can be a struggle with bookings and are still likely to pay taxes and charges that cost hundreds of pounds.
Around 470million people around the world belong to frequent flyer programmes, earning points every time they buy a ticket so that these can later be used on flight upgrades, plane tickets or entry into airport lounges.
The report found the most dramatic process was for a passenger flying from London City Airport to Edinburgh on Air France/KLM, operated by CityJet.
The average return fair costing £115 (only £2 of which doesn't consist of taxes and charges) would earn the passenger 1,000 points with the Flying Blue programme, but they would require 20,000 to cover the £2 portion of the fare not represented by taxes and charges, meaning they would have to fly there and back 20 times before earning the 20,000 required for a reward ticket.
Other disadvantages include restrictions on what flights can be bought with the points as airlines often allocate a restricted number of seats for reward customers. The number of points a passenger earns depends on the type of ticket purchased too. For example, with a discounted fare there may not be any points awarded at all.
Points also often expire after a couple of years if they're not used.
Businessman John Yardley, 61, from Kingston upon Thames clocked up 270,000 Virgin Atlantic points through flights and spending on his credit card.
'I wanted to visit my daughter in Australia, but I spent two years trying to use them, and each time I tried to book I was told there were no tickets available on the flight I wanted,' he said.
'In the end I blew the lot on business class tickets to New York for myself, my wife and our elder son – but I still had to pay nearly £1,000 in taxes and charges.'
Which? travel editor Lorna Cowan said benefiting from frequent flyer schemes required careful planning but were worth joining because most were free.
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