HM - Just because they don't have a dual price list (domestic/EU and international), doesn't mean they shouldn't.
Years ago when I started flying many airlines had a domestic price and an international price for on board alcohol sales. So it has been done, and can very easily can be done.
Not only are they, now including BA, stealing the VAT and duty from their non-EU passengers they are stealing commission from their cabin crew. That is, unless they pay different commission amounts on ex-EU flights. Commission on these flights should be based on gross price, rather than net price. While only a few pennies on a pound it does add up.