BA crew are allowed to buy 6 miniatures on a BA-approved crew purchase scheme if they operate a flight to a destination outside of the EU. If you are caught with minatures but no receipt, it does not necessarily mean you stole the miniatures - just that you have no receipt.
In the past anyone who has bought crew purchase has taken any they didn't drink down route home with them. Once home it was not deemed a necessity to keep the receipt. Apparently now it is.
There has apparently been a much higher number of crew searches since both CC and FC unions expressed enough dissatisfaction with BA management that they started talking about strikes. Go figure.
So to answer the question - Crew purchase IS a legitimate perk of the job. Theft ISN't.