Interview: Deborah Mitford, Duchess of Devonshire

Me neither. Deborah, the 90-year-old Dowager Duchess of Devonshire, and the last of the famous Mitford sisters, is reputed to find class a very boring topic. (The same principle, I suppose, as millionaires finding people talking about their money very dull.) But while we can avoid the "Come the revolution my friends …" kind of analysis, I'm not sure the subject can be – indeed should be – avoided. Just so we know, the Duchess should be referred to as "Your Grace". Should I talk to any of her staff, I should refer to her as "Her Grace" at all times, though there's every chance she will tell me to call her "Debo". (She doesn't, but then I don't call her "Your Grace" either.) As we are all so frequently told, class division in Britain is dead.

The Duchess is both remarkable and formidable. You do not get to be the sprightliest 90-year-old imaginable, sharp and in full control of all faculties ("you'll need to speak louder" is her only concession to age) without being formidable. Nor do you transform the family home, Chatsworth House in Derbyshire, from an inherited debt, complete with 80 per cent death duties, into a multi-million pound business asset and one of the most popular stately homes in England. She is welcoming and charming and, like most people, utterly transformed when she smiles or laughs, but my, those cool, pale blue eyes! That regal manner! I really have to fight to ensure the tougher questions do not become a strangulated squeak somewhere in my windpipe. "Debo" does not capture her at all.

Deborah was married in 1941 to Andrew Cavendish, who became Duke of Devonshire and master of Chatsworth in 1950. The property has now been passed to her son Peregrine. The corridors became simply too long for her, the scale too out of proportion to her needs, so she moved to the Old Vicarage in Edensor (pronounced Enza) also part of the Chatsworth estate. As I am searching for the door into the house, the Duchess's butler Henry pops his head out. "Come through the tradesman's entrance," he grins. Later, the Duchess says Henry has been with her for 48 years. He leads the way through the kitchen, which is warm and rich with the scent of cooking and cooling food, an array of flans and quiches and sweet bakes. Henry hurries to slip on a dark jacket before taking me upstairs, in a scene reminiscent of Mr Hudson in Upstairs, Downstairs.

It is this sense of another time, another place, that makes Deborah Devonshire interesting. Unlike modern celebrities, who write their breathless autobiographies when the first kiss of adolescence is barely dry on their lips, the Duchess has waited until now to publish hers.

Called Wait For Me! it is part personal story, part historical document, with a cast of characters that constitutes a Who's Who of the 20th century. It is not just royalty and prime ministers who dance through the pages – "Uncle Harold" is Harold MacMillan – but writers, artists and designers. Evelyn Waugh, John Betjeman, Lucian Freud, Hubert de Givenchy. Then there's the Kennedy family who were close personal friends. Oh, and Hitler, with whom she once famously had tea.

She makes Hitler sound very ordinary. "He was," she insists, though since she didn't speak German and everything had to be translated, it was perhaps inevitable that conversation would be less than sparkling. It seems not even the powerful are always noticeably charismatic. The Duchess was 18 when she met Jack Kennedy and he was about 21. Deborah's mother told a friend he would be president of the United States one day but Deborah was less impressed. "Danced with Jack Kennedy," she wrote in her diary. "Very nice but rather dull."

The central characters of her early life are her parents, "Muv and Farve", her brother Tom, and of course the other five Mitford sisters: Nancy the famous novelist, author of humorous romances such as The Pursuit of Love; Pam who married a scientist; Diana, the fascist and renowned beauty who left her husband for Oswald Mosley; Unity, another fascist who fell for Hitler and shot herself when war between Britain and Germany was declared; Jessica who became a communist; and finally Deborah, whose cry of, "Wait for me!" was a constant squeal to her older siblings. Why did they capture public imagination so? "It was something that was always an absolute mystery to me," she says. "They were just my sisters. I couldn't understand why anyone was interested in them."

Interesting that she talks about herself almost as an outsider from the rest. Less noteworthy. Less significant. Less anything. "It's terribly difficult to get away from the fact that you are the seventh child and therefore the least interesting to anybody. I was used to not being so much considered." Her mother really wanted all boys (she and Farve never got over it when their only son was killed in the war) and Deborah says – quite cheerfully but seriously – that her birth was such a disappointment nobody looked at her for three months apart from the nanny. Yet while Muv and Farve have been portrayed as somewhat cold and distant in the past, Deborah will have none of it and says it was really to set the record straight about them that she wanted to write her book.

Her mother, she says, was always scrupulously fair despite the crushing disappointment that her girls were not boys. And while Nancy had drawn great inspiration from her father in her fiction, and created a hugely colourful, humorous character, it didn't help portray the real man in a favourable light. "Nancy made him out to be a fearful father with a horse whip, which he wasn't. He could get very angry if we annoyed him too much but I adored him and he was my hero because he loved all the things I did and I used to go fishing with him when I was little."

With the childproof lock on his study (his attitude to women was not dissimilar), his fiery temper and his propensity for saying: "Have these people got no homes to go to?" when he was tired of company, he sounds a volatile man. He moved house frequently as his financial fortunes waxed and waned and was famous for having read only one book.

When Muv persuaded him to listen to her read Tess of the D'Urbervilles, he cried at the sad part before resorting to fury when told it was "only a story". "You mean the damn feller made it up?" he demanded.

Extremes are always interesting. Perhaps that's why the Mitford girls fascinated so, with their unlikely mix of political ideologies. What kind of family nurtured such opposites? But, insists Deborah, her sisters were quite ordinary when you met them and, like many women of their time, merely followed their men. "They were inspired by the people they loved very much. They just followed the men they adored."

Jessica, or "Decca", ran away to marry a cousin, Esmond Romilly, who had fought against fascism in Spain and died in the Second World War.

Decca, too, became a communist. Was that a rejection of her background? "Yes, she was very rebellious. She longed to get away from home. You have to remember it was 80 years ago and she wouldn't have been allowed to have a flat of her own, for instance. These things didn't happen. She didn't have a car and she became very rebellious."

Diana, on the other hand, fell for Oswald Mosley. She and Mosley were imprisoned – in part, together – for over three years during the war.

Only when official papers were released after Nancy's death was it discovered that she had written to the authorities saying Diana was dangerous and should not be released. Deborah thinks Nancy's behaviour outrageous. "I don't know what she was thinking of. It was awful of her. She had no evidence. And she knew perfectly well that Diana had never done anything or would do anything against our country."

Diana was a fascist. Did Nancy not have a certain morality on her side?

Deborah laughs. "No absolutely not! She never had morality on her side. She was tremendous fun, prone to exaggeration, but I don't think she was a particularly moral person." But Diana was supporting a cause that led to the Holocaust. "You mustn't think that all those years, from the 1930s onwards, that these things were known by everybody. It was later they all came to light. Diana had heaps of Jewish friends, so how did that come about?"

Yes, Diana did have "a certain racial feeling", she admits. "But that was all and lots of people felt the same." A certain racial feeling. Did she support the Holocaust? "Oh no, of course not. Of course not."

If I had met Diana, Deborah says, I would have understood. "It was interesting to see somebody sitting next to her who was actually determined to think she was a wicked, dreadful woman, and then in five minutes they had completely melted."

Except Nancy, obviously, who told the authorities her sister was, "a ruthless and shrewd egotist, a devoted fascist and admirer of Hitler", who "sincerely desires the downfall of England and democracy in general". Why did she say those things? "I don't know. Nancy's imagination sometimes went com-pletely over the top. I think, underneath, she had been jealous of Diana's great beauty which is understandable, but she had been so successful in her own career you would think that would make up for everything."

Deborah must feel hurt if she believes Diana, like her parents, has been misrepresented. "It was pretty irritating, I can tell you. The press were awful to her." She still misses Diana and has a huge archive of their letters to each other. Sometimes, she still instinctively picks up a pen to write to her before realising she can't. "She was the one I really liked the best because Decca had gone and Nancy was a butterfly. Nancy was the best company in the world but Diana was the one I really loved."

What were the influences on Deborah's own political thinking? "I had none. I was only interested in what I was doing." She will always vote Conservative, though. "They are much the most sensible and the Labour people are so false now. It would never have occurred to me to vote Labour. As for Liberals, they are too whimsical for words."

The war was a period of great loss for the Mitfords in many different ways. Unity, who admired Hitler so greatly that she sat in a caf he frequented until he noticed her, was distraught at the outbreak of war and shot herself. She survived but never fully recovered and died in 1948, aged 33. Deborah also lost not just her brother but two brothers-in-law and many close friends. "I think anyone who had been through those years came out as different people."

Her parents' marriage was also a casualty of war. It was not just their daughters who were riven by political differences. Muv supported Hitler and disapproved of the war. Farve did not. The once close couple separated. "I was 19. I realise now what it must be like for younger children whose parents separate. It must be shattering, the end of the world. It did affect me deeply but I was on the verge of getting engaged and you know how selfish people are at that age. They only think of themselves really."

Yet, when her father was dying, her mother went to see him one last time. His face lit up when he saw her. "Diana said she would never forget that smile." Did they still love one another? "Well they remained pen pals which was so strange. Sadly we don't have any of his letters to her but we have lots of hers.

Deborah's own marriage to Andrew Cavendish was not without its complications. He was an alcoholic, a subject that was never raised and which Deborah writes about with typical restraint. Acceptance, a lack of expectation that happiness is a right, runs through her book. "I think my generation did accept what happened to them. Lots of my friends had husbands who were addicted to drink and it was pretty evident at times. But they didn't speak about it. Nobody spoke about illness and, of course, alcoholism wasn't even considered an illness then – which it jolly well is. Any form of addiction is an illness and it's impossible to deal with unless the person wants help. You have to wait until they ask you."

She waited a long time for that request. Andrew didn't stop drinking until 1983 and died in 2004. But women then, she says, simply followed their husbands and, to be honest, she wouldn't particularly like to be young now because she likes tramlines, rules, boundaries. Did Andrew's alcoholism make it difficult for her to love him? She doesn't answer that directly but says: "I just felt so very sorry for him. It was very difficult."

The couple had two daughters, Emma and Sophy, and a son they nicknamed Stoker, but Deborah also experienced the sadness of three babies who died at birth. "I described all those babies dying because I just thought it might possibly be a help to some people who have the same experience." It is handled so differently now, I say. Back then, dead babies were whipped away immediately. Now mothers are encouraged to hold them. "I know," she says, "but you know, I could never have done that. I couldn't have faced it." Really? "The idea of holding a dead baby is abhorrent to me."

Some women are shocked by the old attitudes. "I know," she says. Just as she is shocked by the new approach. "I am disgusted by it actually … it must be so agonising for the woman to have this creature put in her arms. I can't understand anyone wanting to do it but I know people do. It's a change of attitude." However it was dealt with, it must have been a difficult time for her. "It was." The two words are spoken very quietly and are full of self-contained sadness.

From an upstairs window of Chatsworth House, inset with square wood panels, the shorn green lawns spread out into the distance, the watery mist from handsome fountains shooting into the air. Chatsworth, a ten-minute walk from Edensor, is a stunningly ornate house on a grand scale; an orgy of marble and oak panelling, of paintings and sculptures, of ceilings heavy with Italian frescoes. A world of tradition and opulence, a world of otherness. Deborah was a driving force behind Chatsworth as a business, though she credits her staff entirely. Up here, I think about why the words "Your Grace" seemed so impossible to say earlier. Some might argue that those who refuse to show deference have an inflated sense of their own importance. I consider that carefully while looking out on the immaculate gardens. I don't believe it's that.

Neither is it about manners. You can be perfectly polite without using titles.

On second thoughts, perhaps it is about manners. Changed manners, changed attitudes, as the Duchess said. She thinks manners are poor now. Ask if her title is important and she says no, it's the inner person that counts. Yet she tells a story that underlines entitlement in her autobiography. Her much-loved friend Sybil, who had "impeccable manners" broke her ankle and was taken to hospital. The nurse came into the room and said "hello". "Not used to being addressed in the modern manner with such familiarity," Deborah writes, "Sybil gave a withering look and said, 'What is all this hello?' and dismissed the nurse with, 'I will ring when my friend has gone.'" Certainly, one of them was horrifyingly rude. Which one?

A wonderful house. Romantic. History is very seductive because it suggests a ribbon of permanence. Across the gardens is the lake from which Colin Firth emerged as Mr Darcy in the televised version of Pride and Prejudice. Extraordinary that once there were no hordes traipsing through it, that it was the property of generations of just one family. The characters who walked these long corridors, whose portraits now grace the walls, who stare down, like My Last Duchess, looking as though they are alive. They're not. And perhaps that's the real resistance to the embellishment "Your Grace". You reach a stage where you understand – truly understand – human impermanence, not just as an abstract concept, and titles become a kind of absurdity. What is a title when a dead baby is placed in your arms? When a dying man smiles at a woman he had seven children with? What does "Your Grace" mean then?

With the reform of the Lords, Deborah says titles have no power any more. She accepts that is inevitable, though she regrets the "brilliantly clever" people the country lost as a result. Her father used to argue that inherited titles made sense because a man who spent his life in politics and public service was more likely to have a son disposed to do the same. Well, not for my money. But what's truth sometimes but a slant, a view, a moment in history? You cannot come to a place like this, meet a duchess, without asking what it all means. And the first thing it means is that class in Britain is not quite irrelevant yet. n

Wait For Me; Memoirs by Deborah Devonshire, John Murray, 20

• This article first appeared in Scotland on Sunday, September 12, 2010