Surprise

A man's walking late at night when he sees a woman in the shadows.

"Twenty quid," she says.

He's never been with a hooker before, so he decides what the hell. 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," he answers indignantly.

"Oh, I'm sorry, I didn't know," says the cop.

"Well, neither did I until you shined that light in her face."