In episode one, series one of "The Thin Blue Line", a 1995-1996 British sitcom set in a police station, one of the characters, Inspector Fowler, played by Rowan Atkinson, uses the expression in conversation. He is saying that his officers do not depend on computers to solve crimes because of their great skills. He says: "They are, in fact, first rate. Keen of eye, swift of thought and regular of bowel. They don't need computers to solve crimes because they have brains."
The addition of "regular of bowel" is a joke. A sudden descent from the lofty to the mundane, and from the relevant to the irrelevant. It is like saying "I admire my teacher. He has a fine analytical mind, he summarises arguments well, and keeps his ears free from wax". Also, toilets are ALWAYS funny. Atkinson often plays characters of the sarcastic sort, and the idea that being "regular" confers health and moral worth is an old-fashioned British belief of the type that is often mocked in modern times.