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Thank you, one and all. Andy - an excellently-constructed answer as always. I guess it boils down to Till Death = racists are stupid; Love Thy Neighbour = racists are funny. Thinking about it, I do remember Johnny Speight telling the story of some halfwit who came up to him and congratulated him for creating a character who said what he (the viewer) felt. "You bloody idiot," Speight replied, "it's morons like you we're poking fun at".
A very good point also raised by kempie - the Reynolds character in LTN was no better than Booth. In fact, you could also accuse LTN of inverse sexism - both male characters were brainless bigots while the women were portrayed as far more intelligent and sensible (I bet I know what all our female contributors are thinking right now!!)
Thanks again for the replies.