I thought that there used to be a rule or something, maybe some unwritten PR pact, that if you appeared on one weekend chat show you couldn't appear on another one. That's why Jonathan Ross and Graham Norton were in compeition to get the big Hollywood stars when a major new movie came out. If one got them the other missed out. Or maybe had to make do with the director, who often turned out to be more interesting anyway.

But this week, if the billings are correct, there is a bit of a once-in-a-blue-moon diary clash. Former Friends star Courteney Cox, who recently said that playing the piano in front of Elton John was the "scariest, most nerve-wracking" thing she's ever done, is set to appear on the Graham Norton Show on Friday night and also John Bishop's show on Saturday night.

And Courteney Cox knows a bit about scary things. She is due to return to our cinema screens soon in a revival of the scary Scream franchise.

On Norton's show Twitter got into a bit of a frenzy about Cox's appearance, suggesting that her face had changed a lot and she resembled Cher, Caitlyn Jenner or simply looked bored.

I'm not privy to the inner workings or the minds of film publicists so I don't know if this has upset or annoyed anyone. Maybe it has been concluded somewhere that John Bishop's show is not a traditional talk show, so there has been no breach of the hypothetical rulebook. After all, he also has stand-up elements and sketches so it could be argued that the format is different and he isn't in competition with Graham Norton.

Anyway, this is probably all only of interest to people in showbiz. If you are a fan of Courteney Cox you wll presumably be delighted to get two bites of her this weekend. And if you aren't a fan you probably don't give a stuff about the previous four paragraphs.

But if you aren't that inerested in Cox, maybe you'll want to tune in for Bishop's other guest, Downton Abbey star Hugh Bonneville. The Harry Potter sar is in a new Netflix thriller I Came By and also the new Red Nose Day sketch.

The John Bishop Show, ITV1, Saturday, 9.35pm.

Picture: ITV1