Prunella Scales is terribly well spoken, a far cry from the screeching Sybil whose laugh was described by John Cleese as "someone machine-gunning a seal".

Only 12 episodes of Fawlty Towers were made, yet Prunella will be forever immortalised as Basil's wife. Perhaps that's why the 75-year old actress works so hard in the theatre, to prove there is more to her than slapstick comedy. Or maybe that's where she's truly at home.

Either way, for her latest part in Gertrude's Secret she's coming to The Theatre Chipping Norton on Sunday, and is happy to chat about Fawlty Towers and the highs and lows of her career.

"Oxford is a very old stomping ground of mine," she tells me, "and I had some really happy times there. In the 50s, just before I got married, I spent two seasons doing rep for the Oxford Theatre Company, with a bunch of undergraduates who are all doing great things now."

Soon afterwards she married Timothy West, whom she chats to throughout the interview, and the pair never stopped touring even when they had two children and an au-pair in tow.

"We could just afford a live-in au pair so when the children were young, well I was still breast-feeding, we took them all with us.

"We did the sums and decided it was still worth it and much better to do that than one of us to sit at home. It seems to have all worked out. They're all still speaking to us ..." - and she tinkles with laughter.

"But I teach drama now and I always start by telling my students: 'save your money for taxes and for the times when you're not working and be careful with your money'."

Prunella has been London-based all her married life and has no desire to up sticks and return to the country, where she grew up.

"To get anywhere I had to walk half an hour through the woods to catch a bus to get on the train," she recalls.

"So when my uncle gave me his stamp collection I sold it for £308 which kept me in digs in Dulwich for a year, and I haven't left London since," she says.

Her early film roles included Pride and Prejudice and Hobson's Choice and her first career break came with the early 1960s sitcom, Marriage Lines, with Richard Briers.

But once Fawlty Towers came along Prunella was in a much better position to choose her roles.

"I saw the script and went in to see John (Cleese). He was ill with the flu and I said, 'I have one question for you - why on earth did Basil and Sybil get married in the first place? 'Ah,' he replied. 'I was hoping you weren't going to ask me that'."

She laughs. "I told him I thought Basil had met Sybil once he'd left public school and maybe National Service, and wanted to buy a hotel with his demob money.

"She was working class and I think they met while she was working behind a bar so she was the one who knew how to run the hotel, because her parents were in the business.

"That's not how John had seen her at all, but they let me go with it," she says.

So did Prunella have any idea how big Fawlty Towers would become? "None at all ... we did six episodes and were then commissioned to do another six."

And did it have an immediate effect on her career? "Well, programmes like Fawlty Towers and a few others help because it means the general public are willing to step off the pavement and into the theatre if they've seen you on the TV."

Which she hopes they'll do for Gertrude's Secret - a series of short stories which Prunella won't tell me any more about. "I can't it would give the game away," she tells me.

"But celebrity is the worst word in the English language to me," she adds, "I hate it, because a part should be about the morality of the play and about the meaning and about the delivery ..."

So she doesn't mind that there are posters everywhere around Oxford advertising Gertrude's Secret with pictures of her looking rather tired in an old dressing gown.

"Why on earth would I?" she asks, in genuine surprise. Sybil would be proud.

Gertrude's Secret plays at The Theatre Chipping Norton on Sunday. (Box office on 01608 642350.) It moves to the Oxford Playhouse in August.