Dig out your old boarding passes – BA and Virgin passengers can now register for a refund of illegal fuel surcharges made by the airlines.

The two carriers were found guilty last year of unlawfully conspiring to fix the price of fuel surcharges, and, in addition to multi-million pound fines, both airlines have been forced to offer refunds to passengers affected by the charges.

This means that any passenger who purchased transatlantic or other long-haul flights over seven hours departing from the UK with either BA or Virgin, between August 11, 2004 and March 23, 2006, is now entitled to a partial refund of up to £20 per flight.

If you believe that you qualify for a refund (and there are up to 5.5 million of you out there), your first step is to register your details (either as an individual or business) at airpassengerrefund.co.uk. The airlines says you will then be contacted “in the coming months” in order to fill in a written or online claim form.

It’s not clear at present what details you will need in order to make your claim, so frequent flyers are advised to dig out any records they may have of flights taken during these periods. It is understood that law firm Cohen, Milstein, Hausfeld & Toll, who brought the class action lawsuit against the airlines, has been given passenger lists of al those who travelled with BA or Virgin during the affected periods.

Any unclaimed monies will go to charity, although the £73.5m fund for passengers travelling from the UK will stay active until 2012. Passengers who bought tickets from the US during the affected period should visit airpassengerrefund.com.