Some airlines are "ripping off" travellers over refunds for the Air Passenger Duty (APD) airport departure tax, a consumer group has said.

A number of carriers have withheld "tens of millions of pounds from their customers" in refunded APD when passengers have booked tickets but not flown, the Air Travel Advisory Bureau (ATAB) said.

The bureau has now joined forces with London law firm Barket Gillette LLP to fight on passengers' behalf.

ATAB chairman Tony White said: "It is a scandal that some airlines hang on to this money. It never belonged to them. It's a tax collected on the behalf of the Government.

"With a couple of exceptions, most of the UK airlines make it as difficult as possible to get your money back. If you don't actually fly, for whatever reason, you are entitled to get the APD refunded."

Mr White continued: "It is truly shocking (about what goes on). We've found some airlines that will charge an 'administration fee' greater than the value of the refund. This is a complete rip-off and it's our intention to put an end to it.

"If you have booked an airline ticket out of the UK anytime since 1994 (when APD was first introduced) and not flown, then we want to hear from you."

Barker Gillette LLP partner Steven Barker said: "Our primary aim will be to ensure that all claims are valid and properly made out. We hope and expect that airlines will co-operate with us in agreeing and refunding valid claims and that claimants need only seek the assistance of the courts in respect of legal issues that might not be agreed."