The Dowager Duchess of Devonshire: Chatsworth's 'housewife' looks back

Being a duchess doesn't save you from official forms. "When I had to fill in my occupation, I used to put 'housewife'," says the Dowager Duchess of Devonshire. "Because that's what I was: the wife of a house... Well, three houses, as it happened."

There was Bolton Abbey in North Yorkshire, Lismore Castle in Ireland, and, most publicly, Chatsworth, the great Derbyshire house that has defined stately home-going for half a century.

After her husband Andrew died in 2004, the Dowager Duchess, less formidably known as "Debo", moved out of Chatsworth – which is marking her 90th birthday next month (March 31) with a new exhibition – into a more manageable former vicarage. "I tried to bring over what I loved most," she says. "Chatsworth's furniture was mostly grand and wouldn't do in a small house. I've lived in furnished rooms since I was married, but none of it was mine."

Her new home is full of cosy cultural clutter, boxes stacked in corners, papers heaped in baskets, family snapshots, books everywhere. When her butler, Henry Coleman, who retires this year after almost half-a-century at Chatsworth, brings me a glass of water, he has to balance it perilously on the two foot pile of hardbacks on the coffee table. Joining them in the autumn will be the Dowager's autobiography, which she has recently finished, though she says she keeps remembering more things to put in.

Her life falls into three phases – the early years, as one of the celebrated "Mitford girls" (written about often, or, as she pronounces it, "orphan": a voice from a "lorst" age); 46 years living at Chatsworth, which reopens on March 14 after its most extensive facelift in almost 200 years; and now her new home.

Its compact size ends her years of long-distance walking in the big house, where it could seem a good half-mile from her private quarters to the kitchens. A few years ago, interviewing her about her new cookery book, I tried to keep up with her as she made this marathon journey.

Much of it was along private corridors, but every so often she opened a door and we emerged in the public areas. Visitors were sometimes alarmed as the doughty Duchess strode past them over rope barriers beaming "Good morning!" Some froze, some mimed a vague curtsey, none reached for their cameras. She may be a celebrity, but you don't do anything as vulgar as take snatch pictures of her.

She claims small credit for Chatsworth's success, but to many people, I suggest, she is Chatsworth and Chatsworth is her. She put herself about, was always available to the media, always obliging, always full of good quotes and good fun.

"Well, for many years I had no position at all except as the wife of the person in charge. But I suppose I was always around, chatting to people in the garden. Once there'd been a television programme or two, people tended to recognise me." And it was, she says, only courteous to be pleasant to visitors who had come to see the house.

How did she feel about leaving it? "It was very odd, rather than a wrench. Of course I knew it would happen if Andrew died before I did. It was entirely expected." And there's a hint that the line of inquiry is closed. She dislikes the modern fashion for emotional self-indulgence and "lack of manners", though seems less worried by the gradual dwindling of deference, which started, she thinks, in the Sixties.

Nor do you get very far with inquiries about how aristocrats fit into today's world. "The whole thing about what they call 'aristocracy' is ridiculous," she says. "It's quite a barrier with some people and it's a perfect nuisance. Aristocrats aren't legislators any more. When they were, they were extremely important. My sister Nancy used to write about it..."

The changes she has seen in society will be reflected in Celebrating Deborah Devonshire, the exhibition about her, which will feature cherished personal possessions. "We've discovered the nature notebook I had as a child. I suppose I was about 10 and I got a bit stuck with the sedges. And there are my skates. Skating is the only thing in my long life I've been able to do well.

"That's one excitement. Another is my gun. The keeper had it. I used to spend the whole winter shooting, when it was very unusual for women to shoot. It was like a man's club, the shoot. I only gave it up recently. I think I shot my last grouse in 2003, up at Bolton Abbey. And there are little bits and pieces of life, like dressing up for the Coronation in 1953." Her Coronation robe was originally designed for the celebrated Duchess Georgiana in the 18th century – "the most wonderful velvet, off the shoulder and absolutely different from what anyone else was wearing. We went in the coach..."

A surreal vision of the Duke and Duchess arriving at Westminster Abbey in a precursor of National Express flashes to mind. But no. We're talking horse-drawn coaches, royal-style. "There were only four private coaches – us, the Duke of Wellington, Lord Bath and one other. It was very grand and there was very little room in it, but it was something for the crowds to look at; some of them had been there all night. But we got lost. The coachman had never been to London before. Eventually Andrew put his head out of the window and shouted 'Left, right, first left' and of course the crowd were absolutely delighted."

And then a memory of the Abbey: "All the ranks of peeresses, like a sort of dream, like something in a ballet; an amazing phalanx of these women in their Coronation robes."

The exhibition will also include souvenirs of her unlikely obsession with Elvis Presley. "There's a telephone; instead of the bell ringing it plays Jailhouse Rock, and there's a bit of the fence from round his house. I knew a woman who was his neighbour and she gave it to me. He was so beautiful when he was young. In the Inigo Jones sketchbook at Chatsworth there's this young man who looks just like Elvis..."

I say I recently saw her described as "a national treasure". How does she feel about that? "A terrific exaggeration. We're not all national treasures because we're 90."

It prompts a typically self-deprecating story about a newspaper commissioning her to write a 500-word article. She wrote the piece, sent it off, and subsequently had a phone call from someone at the paper. "He said: 'You use such short words that it doesn't fill the space.' I said: 'Short words? I don't know any long ones'."

The Duke and the reopening

In Chatsworth's Lower Library, surrounded by dcor from George II's day, the Duke of Devonshire pours the coffee and reflects on the house he inherited six years ago after his father's death.

"Don't forget that it was built to show off," he says. "It was designed as a 'wow', saying 'They must be important people who live here'. What my parents did was very gradual, a very measured process of turning a private house that was opened to what was then called 'the public' into

a 'visitor attraction'. It became a place for visitors first and the family second."

Many of them are visitors for whom Chatsworth is a part of their own lives. A change to a restaurant colour scheme (the new Duchess is fond of bright colours) can prompt letters of outrage from Disgusted of Derbyshire.

No such letters are likely when the house reopens next month. It will still be the old Chatsworth – acres of gilded splendour, tapestry by the square mile – but more of it will be on show than ever before thanks to a 14m restoration and development project.

Simon Seligman, Chatsworth's head of communications, tours me round what was still effectively a building site when I visited several weeks ago. A new lift has been installed to improve disabled access, exhibitions will draw on "treasures from the vaults" and celebrate the Duchess Georgiana, family and royal portraits have been dusted down. New galleries and a new visitor route have been created, windows blocked since 1830 have been reopened, a previously private courtyard made accessible and a graceful lighthouse-like lantern revealed after being sealed for a century. "Up there was very, very dusty, but it was in very good condition," says Seligman.

We step gingerly into the Sabine Room, covered with depictions of the Abduction of the Sabine Women, complete with fleeing victims and wild-eyed horses. Once used as a guest bedroom, it doesn't instantly seem to guarantee an untroubled night's sleep, but as Seligman says: "The old Duke used to sleep in here on a camp bed at Christmas."

Back in the Lower Library, the new Duke recalls those times: "Before the war, the house was much lived-in for certain parts of the year, and at Christmas it was full to the rafters. People brought their ponies and their nannies. It seems very long ago."

He says 138 staff were employed in 1950. Now there are 500, thanks to the visitor business, the farm shop and restaurant. So why do visitors come? Chatsworth surveys have reached some unexpected conclusions. "The house wasn't in the top five reasons. What stood out most was the landscape, which was a major surprise to me because we take it for granted."

Has the Dowager Duchess been a hard act to follow? "It's a different act. It would be impossible for us to have the ideas and the innovations she had. She and my father rescued this from being a sad place covered in debt to being a happy place."

Chatsworth House reopens on March 14. Tel: 01246 565300; www.chatsworth.org