I once worked in Duty Free at Gatwick North Terminal, and after the Docklands bomb in early 1996, armed police became much more visible.
I remember one instance where a Norwegian customer had missed his flight to Oslo at 8am, and there wasn't another until 8pm. He was wandering around the terminal, in and out of the shops, generally just killing time, but at one point I saw him pick up a bottle of whisky and put it inside his coat.
I watched where he went to sit, and went to ask him for the whisky back.
'I don't have your whisky. I didn't take anything. I'm a good man!'
'You did take it, I saw you. Just give it back, and there'll be nothing more said.'
He refused, so, as I knew he couldn't really go anywhere, I left him be, thinking that I'd get security or the police to have a word when they next came around.
About an hour later, two armed policemen came into the shop. I pointed out the guy who was by now asleep on the seats, and asked if they could go and have a word with him. I didn't want a fuss or to press charges, I just wanted the whisky back. No problem, they said.
So they go over, shake him by the shoulder to wake him up, he opened his eyes, sat bolt upright and immediately delved into his coat to give them back the whisky.
When they brought it back into the shop, they were both laughing and I asked what was so funny.
The policeman said 'As soon as he opened his eyes, the colour drained from his face, he sat straight up and said 'It's only whisky! No need for machine guns!'.