Looking for a film I saw on TV in the 70's or early 80's. It's about a woman who is a mechanical engineer and works for an aircraft company(?). Because of her profession she cannot find any dates, but her biological clock is ticking and she decides to have a one night stand and get pregnant. She goes to the local pub and befriends an unlikely guy. I think she pays him to sleep with her. She has a child as a single mother.

Can't remember if it was BBC or ITV, but the subject was treated very nicely and I would like to see it again.

Any ideas?