Just watching the ITV programme on currently hoping for an answer without success.
In the 1970s whenever I was back in London I used to listen to his Sunday night radio show on LBC; this was a rolling trivia quiz, years before trivial pursuit or pub quizzes took off.
One thing that I always remember him saying was that he was responsible for something that was nationally well-known every year but was in fact a hoax (or that's the way I remember it).