A man walking home late at night sees a woman in the shadows.
"Twenty quid . ."she whispers.
He'd never been with a hooker before, but he decides, what the hell, it's only twenty pounds. So they hide in the bushes.
They're going "at it" for a minute when all of a sudden a light flashes on them it's a police officer.
"What's going on here, people?" asks the officer.
"I'm making love to my wife," the man answers indignantly.
"Oh, I'm sorry," says the cop, "I didn't know."
"Well," says the man, "neither did I, until you shined that light in her face".