Talking Radalt,
I fully believe you about big Blue and the like, but what industry do isn't necessarily right for us. Fine, financially, it may make sense to accept "a bit on the side" - but as far as I'm concerned, we work in an organisation that exists on trust. Trust that our mates will look out for us, trust that the orders that send us into danger are the right ones and trust in the "team" as a whole.
Fraud ('cos that's what it is, not a "perk"), erodes that trust - so I don't give a monkey's what the financial experts say - if you're a cheat then you don't deserve to wear the Queen's uniform; and if it costs money to weed these people out, then it's money bl**dy well spent.
However, I share the concerns about the honest mistake, I rarely put a claim in without getting an admin bod to give me the thumbs up - dunno what I'll do when there's no-one left!