Their lives have charted, albeit sometimes in caricature, the vicissitudes of a nation and the forces which have buffeted it. The story of the Mitfords is the story of Britain in the 20th century.
Unity Mitford fell in love with Hitler, and shot herself. Diana married the British fascist leader, Sir Oswald Mosley. Their brother Tom was killed fighting in Burma in the Second World War. Nancy, the socialist novelist, died, rejected, in Paris in 1973. Deborah joined the grandest stratum of English aristocracy, marrying the Duke of Devonshire. Pamela, wooed by the poet John Betjeman, married the son of a newspaper magnate. And Jessica became a communist and then went to live in that bastion of anti- communism, the United States.
"The Mitfords were not so much a photograph of their times, as a cartoon," says Ned Sherrin, the writer and impresario behind The Mitford Girls, a musical based on the family. "They represent a heightened picture of every section of English society, all extreme in one way or other."
They were wonderful anachronisms, resolutely Thirties English upper- class gels in a world of change which they accommodated without ever fully accepting.
The sisters grew up in a classic upper-class country house - Swinbrook, in Oxfordshire, the family home of Lord and Lady Redesdale. What made them remarkable was that - never being sent to school to mix with other children of their class, but stimulated by the sharp, jealous intelligence of Nancy, the eldest, they grew up in a world of ferocious intimacy, private nicknames, intense competition, exhibitionist fervour and unbounded self-confidence.
If Nancy was the cleverest, it was Diana, the most beautiful, who seemed destined to make most waves in Thirties society. Among her associates were Lytton Strachey, the Sitwells and Evelyn Waugh - his novel Vile Bodies is dedicated to her.
Scandalously, for those times, Diana divorced her husband Bryan Guinness (later Lord Moyne) to make herself available to the married man she had fallen in love with. He was Sir Oswald Mosley, then described as the cleverest man in the House of Commons. He later quit the Tories, then Labour, and formed the British Union of Fascists; his Blackshirts stalked the streets of England.
Diana married him in Berlin in 1936. The wedding reception was given by Magda Goebbels, wife of the German minister of propaganda. Adolf Hitler was present.
But when war came the Mosleys were interned; they later went into exile in France in their ironically named home La Temple de la Gloire, just outside Paris. Diana lives there yet - elderly, beautiful (she still has piercing, cornflower-blue eyes), polite, unapologetic and proud.
Only she and "Debo", now mistress of Chatsworth, and the peacemaker among the family, survive. There was much peacemaking to do. Diana's link with Hitler had been affected by her younger sister Unity, who became so besotted with Nazism that she went to Germany and sat in the restaurant where he regularly lunched, until she was invited to join him.
It was the first of 140 meetings which the moonstruck Unity recounted with girlish gush, calling Hitler "sweet" and "an angel" and thinking it thrilling when he ranted and raved against his underlings.
The day Britain declared war she went into a park and shot herself, though it took her eight years to die from the injuries. "Say Not That The Struggle Naught Availeth," the inscription on her gravestone declares.
Tom, who, Jessica claimed, had introduced three of his sisters to the sexual act, perished in the war which Hitler started.
Nancy, who denounced her sisters to the wartime authorities, went on to write a number of novels, period pieces whose surreally snobbish characters depict England in the last years of the empire.
She also made an enduring contribution to British literary sociology, in 1955, with her essay in Encounter magazine on "U and Non-U", parodying codes of upper-class and non-upper-class speech.
The other sisters thrived in their chosen worlds. Pamela, who died in 1994, divorced from scientist Derek Jackson, the son of one of the founders of the News of the World, lived quietly in the country, breeding the Appenzeller Spitzhauben hens she had introduced into Britain from Switzerland.
Against such a background it seems unremarkable that Jessica - who had been saving her "running away money" since childhood - should have eloped at 18 with her cousin, to the Spanish Civil War. It was the start of an involvement with the Left which separated her from her sisters - she hardly spoke to Diana for more than 40 years.
"It was not just a game," says a friend, Polly Toynbee. "She was a hard- bitten communist. She believed it deep down, even after the invasion of Hungary. It was almost an act of faith."
But faith went out of fashion. As she got older Jessica exercised her disdain for authority in elaborate ruses to avoid paying for train tickets or telephone calls. "She would often arrive waving airline cutlery she had stolen while travelling first class on some magazine commission," recalls Toynbee. "Freebies were her idea of revolution."
Thus the Mitford saga, like the epoch it echoes, ends in self-parody. It is part of its joy that the Mitfords shared the joke. When their mother, Lady Redesdale, was dying, she summoned Jessica to her bedside and said: "I've left all my money to your sisters ... You have never had money anyway and never cared about it, and you know how the rich do love money."
For years afterwards, Jessica quoted the words with evident approbation.
Obituary, page 16