I wonder if this is actually a VAT or Duty issue on what is carried onboard BA or not? On each flight, you need to remember there is a set limit of number and value that is carried onboard, sure passengers will have their own limits but the airline has already agreed with the govt and trading regulations of each destination country.
Crew can be equally guilty of theft and some also have gone as far as sharing raids within the hotel rooms for pre-drinks before hitting the nights out and have broadcasted this on their social channels, though in recent times this has scaled back.