(You might need to be a Brit to understand the punchline...)
An elderly couple go to a sex therapist's office. The doctor asks, "What can I do for you ?", and the man replies "Would you monitor us having intercourse, please ?" The doctor raises both eyebrows, but he's so amazed that such an elderly couple are seeking his assistance that he agrees.
When the couple finish, the doctor advises "There's absolutely nothing wrong with the way you're having intercourse".
He thanks them for coming, wishes them good luck, charges them £50 and says goodbye. The next week, however, the couple return and ask him to watch again. He's a bit puzzled, but it's all money, so he agrees. The visits are repeated several weeks in a row. The couple make an appointment, have intercourse with no problems, pay the doctor and leave.
Finally, after 5 or 6 weeks of this routine, the doctor says, "I'm sorry, but I should ask: just what are you trying to find out ?" The old man says "We're not trying to find out anything. She's married and we can't go to her house. I'm married and we can't go to mine. The Holiday Inn charges £98. The Hilton charges £139. We do it here for £50, and I get £43 back from BUPA".