British Airways customers are being urged to use their Avios to book reward flights before the scheme changes on May 27. Avios is the loyalty scheme of more than 30 major airlines, including British Airways , Iberia and Aer Lingus. It allows you to build up points which you can then exchange for flights, although you still need to pay taxes and fees. But the cash amount you have to pay towards a reward flight with British Airways will rise from this date, warns MoneySavingExpert.com - which