Thanks for the explanations. Although a bit before my time, I discovered the mp3 recordings of 'Round the Horne' many years ago, and they seemed to use them all the time. In an interview, somebody mentioned that the writers used them more and more to get dirty jokes into the script without getting into trouble. He reckoned that most sailed right over the producer's head, and he often didn't understand why the audience were in hysterics.
One I remember is from the famous Sandy & Jules sketches with Kenneth Williams and Hugh Paddick. In one sketch, they explain to Kenneth Horne how they're working as a legal team. When asked what they're currently doing, Kenneth Williams says something like, "Well, of course, Jules and I are usually involved in certain illegal activities."
The audience cracked up. Homosexuality was still officially illegal but everyone knew that they were both gay.
Steve
PS The main writer then was Marty Feldman, an absolute genius!