Originally Posted by RJB
Taxes at Heathrow are substantially higher than at Luton.
BA also includes some other spurious charges, such as its fuel surcharge, in with taxes. If you try to book the same BA flight on aa.com you'll find it is cheaper because AA doesn't add on one of BA's funny extras.
Try comparing taxes, charges, surcharges, sursurcharges, captain's bacon sandwich etc where BA and EZ use the same airport, e.g. LGW. EZ's charge for flight plus extras can often be less than BA's charge for extras alone.
RJB's second paragraph is the answer. BA choose to class as extras charges included in some other airlines' fares.