Airlines are being accused of keeping millions of pounds for themselves which ought to be refunded to passengers.

Anyone who fails to take a flight they have booked should be able to reclaim the tax element.

But the consumer organisation, Which? says most airlines make it too difficult to get that money back.

"In some cases it costs at least twice as much to reclaim the tax as the tax itself," says Which?'s Rochelle Turner.

In most cases passengers who miss, or deliberately fail, to catch a flight, are unable to reclaim the cost of the flight itself.

But they should be able to reclaim the Air Passenger Duty (APD) which varies from £11 per person on a flight within Europe, to £110 for a long-haul first class flight.

A family of four flying economy from London to Miami currently pays £200 in the passenger tax.

Most airlines charge passengers an administration fee if they wish to reclaim the tax.

Ryanair, for example, charges £17 per person while Flybe charges £25. Both Virgin and BA charge up to £30.

Among the major airlines, only Easyjet will refund the tax for free.

This means that unless passengers are paying a higher rate of the duty, such charges make it impossible to reclaim.

"I think it's lamentable that the airlines can impose such high charges," says Simon Calder, travel editor of The Independent newsaper.