Yes, Pete.  It's a clip from Radio 4's 'Dead Ringers', I believe.

I used to love the thing they did where Alan Bennett would come on and say something like - "Last week, as Thora Hird and I were sharing a pot of Earl Grey and a small plate of custard creams..."  He would go on to recount the tale of their time as head honchos in an international drugs cartel, or some such unlikely scenario.

I just finished reading Alan Bennett's memoirs, and he says he always enjoyed those sections too!

I know what you mean about that John Culshaw though - there's definitely something of the knob about him!