Extra marital sex

An elderly man and woman, both in their 70's, walk into a sex ther****t's office.
The doctor asks, 'What can I do for you?'

The man says, 'Will you watch us have sexual intercourse?'

The doctor raises both eyebrows, but he is so amazed that such an elderly couple is asking for sexual advice, that he agrees.

When the couple finishes, the doctor says, 'There's absolutely nothing wrong with the way you have intercourse.'
He thanks them for coming, wishes them good luck, charges them £50 and says good bye.

A week later the couple returns and asks the sex ther****t to watch again. The sex ther****t is a bit puzzled, but agrees.

This happens several weeks in a row. The couple makes an appointment, has intercourse with no problems, pays the doctor, then leave.

Finally, after 3 months of this routine, the doctor says, 'I'm sorry, but I have to ask.
Just what are you trying to find out?'

The 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 my house.
The Holiday Inn charges £98. The Hilton charges £139.
We do it here for £50, and I get £43 back from BUPA'