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I know that in this day and age it just wouldn't look convincing if the same actors played different parts in sitcoms or dramas, but I know that throughout the 60s and 70s (and even into the eighties) a number of British and American series sometimes used the same actors in different guest roles.
I have seen on the Internet Movie Database that a few actors played different parts in series such as Z-Cars. There are a quite a few sitcoms featuring the same actors in different roles but I can only think of one off the top of my head and this is the most ridiculous example:
I saw a few episodes of Terry and June in the early 90s on UK Gold when my parents watched the series. I was never a fan myself
but I remember noticing that Terry's friend and colleague Malcolm was re-cast in later series. In one of the last episodes Terry, June, Malcolm and Malcolm's wife are at a party held by Terry and Malcolm's boss (who had servants!) and there was a drunk butler who was played by none other than the previous "Malcolm" actor who had only left two series before!
Did producers and casting directors think that viewers wouldn't notice? It is a bit like re-casting Peter Howitt as a policeman in one episode of Bread two years after he quit playing Joey Boswell!
I have seen on the Internet Movie Database that a few actors played different parts in series such as Z-Cars. There are a quite a few sitcoms featuring the same actors in different roles but I can only think of one off the top of my head and this is the most ridiculous example:
I saw a few episodes of Terry and June in the early 90s on UK Gold when my parents watched the series. I was never a fan myself

Did producers and casting directors think that viewers wouldn't notice? It is a bit like re-casting Peter Howitt as a policeman in one episode of Bread two years after he quit playing Joey Boswell!