Had an experience a few years ago, after I'd forgotten to take something or other out of my case. Security happened across the envelope with nearly £10,000 in, which I was using to buy a car in a couple of days time.
It got put to one side, and a nod to Special Branch (I was flying out to Northern Ireland). We had a chat about the car, a brief look at the limited paperwork, and was congratulated on my choice and the deal.
No problem really.