Absolutely Disgusted it is a personal choice, but the fact still remains that in 2010, knowing about anti money laundering, proceeds of crime act, along with the fact that cash is available securely from nearly every major airport in the world, for as little as £5 a throw, it is an acceptable question to ask, why would someone carry an amount of cash above even £500.
You could have a casino win (thats one explanation), but carrying your expenses for a 2 week trip in cash, I think is peculiar in todays society. If my company gave me a brown envelope for my trip expenses, I would not accept it.
I believe that even aircrew are now given their trip expenses in plastic, I may be wrong, but the last time I was with some friends from BA down route, they had to go to the hotel with some plastic to obtain their “dinner money”.
By all means have a personal preference, but do not be suprised if your personal preference raises questions.