I'm guessing
Since Domestic and Int'l passengers are mixed in T5, I'm guessing it's because they don't pay VAT on purchases made by Int'l passengers for books and water, but they do for Domestic passengers. Seeing your boarding card allows them to press the correct button on their till.
Does this mean they are charging you the VAT but not paying it to HMT? Your guess is as good as mine.
BTW - Why are you buying water? Take an empty bottle with you and fill it up at a water fountain or in the loo.
Stand to be corrected, BUT
AFAIK VAT is not currently chargeable on Books/Newspapers or
plain Water in the UK
PZU - Out of Africa (Retired)
AS someone who has sworn never to transit Heathrow again - am considering a T5 transfer - am I being rash???
