I think this is possibly the litmus test

[burntcopper]

How to tell you're a radio 4 listener : Never mind the news and such, you know what Mornington Crescent is.

a regular listener : you know the rules.

have been listening far too long : you readily participate in the game whenever given the chance.

may possibly have an 'I love Humph' badge : you quite happily become part of the audience and make encouraging noises and know exactly when to do that indrawn breath.

All evidence here : http://kabukivice.livejournal.com/407206.html

Comments

[sabremeister]

Have you seen the rather simplistic explanation of the game at http://www.hp-lexicon.org/essays/essay-in-search-of-grimmauld-place.html?

(Incidentally, it suggests that Grimmauld Place is near Camden Town, so keep a look out for it...)

[davidcook.livejournal.com]

How to tell you're a radio 4 listener ...

... or had maths-juggling-music geek friends who knew about it and passed it on. (I was in Oz at the time, no radio 4 there, alas - nor anything quite like it)