This was first shown on Channel 4 here in the UK in about 1985, I don't know if it was ever repeated. I missed it then and it wasn't until I read the books several years later that I started to look out for it. I recently got the entire series on video (would have been better on DVD) and it is a hoot.
The main characters were just as I pictured then and the casting was spot on. Geraldine McEwen (not yet a Dame alas, apropos a previous comment) and Nigel Hawthorne (who is indeed Sir Nigel) shine as Lucia and Georgie but perhaps they had easier characters to portray and it is Prunella Scales as Mapp who give the best and most difficult characterisation, though all the parts are really caricatures. Everyone must have had such fun making this and Lucia's costumes are something to behold.
The exteriors are mostly Rye in Sussex, where the author E.F. Benson lived (and was the Mayor). Lucia he probably based on himself, which begs the question who was Georgie in real life?!. You can go to the house he lived in which was clearly Mallards in the books and is now National Trust property. Henry James lived there before him. However, it wasn't used as the exterior here.
Some characters from the books are dropped in the series, the Padre's wife and the Wyses's daughter, but you don't miss them. Traces of McEewen's power mad and devious Lucia can be seen in her portrayal of the mad religous mother in 'Oranges are not the Only Fruit' (1990).
Sip tea and cakes with friends on a wet Sunday afternoon as you watch this - it'll cheer you up no end.