MacCarthy was among the last 18-year-old girls to curtsey to the Queen, in March 1958. That was the last year in which nubile, submissive young women performed this arcane ritual signifying that they had "come out" - marking the aristocratic virgin's rite of passage from schoolroom into society, and signalling that she was marriageable. "What a cattle market it was," MacCarthy says.
The Season, as it was known, went on for months across England, Ireland and Scotland and in her own case, she says, is to blame for her becoming a workoholic - and for her "many subsequent symptoms of excess". A noted journalist, design writer and award-winning biographer, whose subjects have included Eric Gill, William Morris and Lord Byron, she was so exercised about having taken part that for decades it seemed "worryingly shaming", especially when she was working for the Guardian as a feature writer during the 1960s.
No-one was going to brand her an ex-deb amateur: "Would I, for instance, have felt the need to spend eight years - eight years - researching and writing the life of Byron, reading every single letter that he ever wrote, leaving not a stone unturned in the Byronic haunts in Italy, Greece and even Aberdeen, if I had not been disowning my own past life as a debutante? Maybe; but I think most likely not."
Last Curtsey is a revelation, vividly conjuring up the long-lost world of debs' mothers' lunches of chicken in white sauce, cocktail parties, coming-out dances, the descent of the virgins down the staircase at Queen Charlotte's Ball, the Fourth of June at Eton, Royal Ascot, high jinks in Highland bothies, and being groped by "debs' delights" - eligible and sometimes ineligible bachelors - in taxis.
Stylishly written and witty, it is also an important historical and sociological work that is surprisingly poignant, tracing the profound changes to the expectations of women over the past 50 years. Back in 1958, she points out, it was a different world. Krushchev came to power in Russia that year; Prime Minister Anthony Eden had resigned over Suez the year previously, and it was only two years since John Osborne's Look Back in Anger.
Yet here were hundreds of "silly girls", dressed like their mothers in petal hats and long kid gloves, with corrugated permed hair, wearing rubber "roll-ons" (impregnable girdles with suspenders - "no wonder we were virgins!") beneath their full-skirted, calf-length dresses, lining up at court in court shoes to make obeisance to the monarch, something the daughters of the aristocracy had been doing for the past couple of centuries. MacCarthy recalls that she wore wild-blue silk, the favoured fabric of the 1958 Season.
"It was such a peculiar thing to have done," one former debutante remarked to MacCarthy recently. "Peculiar indeed," she murmers. We're sitting in her minimalist living room, gazing at collections of sepia-toned diaries and scrapbooks. Ghostly memories drift up from dusty pages filled with yellowing invitations to an endless round of luncheons, parties, dances, Highland balls and Gosford Park-style country house weekends. There are newspaper cuttings, pages from Jennifer's Diary in Tatler - house magazine of the posh and privileged - and faded fabric swatches of long-forgotten frocks, carefully preserved alongside crumbling pressed flowers presented by long-forgotten beaux. These precious objects have been loaned by several of the debs who curtseyed alongside her - she kept no such souvenirs.
The curtsey itself was all part of the mystique. "It was a question of leg-lock: left knee locked behind the right knee, allowing a graceful slow descent with head erect, hands by your side. Avoidance of the wobble, definitely frowned upon, relied on exact placings of the knees and feet," she reveals.
The technique had been passed down through generations of debutantes, who learned it at Vacani's School of Dancing, at 159 Brompton Road in Knightsbridge, a few blocks down from Harrods. It's where MacCarthy's late mother, Yolande Yorke Fradin de Belabre - "the girl whose name reminded gossip columnists of the heroine of a medieval French romance" - learned her curtsey in 1925, when she was presented at Buckingham Palace wearing the then obligatory ostrich feather headdress and white dress with long train.
Madame Vacani, "who had something of the manner of a genteel sergeant major" as she trained prospective debutantes, would urge: "Now darlings, throw out your little chests and burst your little dresses." Once learned, never forgotten, like bicycling or skiing. "I believe I could achieve a Vacani curtsey still," writes MacCarthy.
Thanks to a 1990 reunion, which gave her both "a sharp, sad stab of dj vu" and the original idea for the book, she discovered that some of the 1,441 girls who made their curtseys with her in that final year have had brilliant careers as businesswomen and educationists; then there were Jennifer Murray (the former Jennifer Mather), who became the first woman to pilot a helicopter around the world; and the radical revolutionary Rose Dugdale, jailed for her nefarious activities on behalf of the IRA.
Teresa Hayter once held the record for party-going and was a bridesmaid at MacCarthy's wedding to Ian White-Thompson in 1961 - a brief marriage that "was really just an extension of the Season" and which ended in divorce. Hayter transformed herself from dizzy debutante into International Marxist.
And the vivacious Scottish debutante,Tessa Prain - whose evocative photograph with fellow deb Ann-Carrington-Smith (with whom she shared her coming out dance at the Prains' 17th-century home in Mugdrum, near Newburgh in Fife) adorns Last Curtsey's dustjacket - became Mrs Vere Fane, later Marchioness of Downshire, and a successful professional interior decorator.
Dressed in a copy of a Balenciaga ballgown executed by an ingenious dressmaker, and long white gloves, she's the archetypal girl in pearls. She sums up that bygone era for MacCarthy, who recalls that Prain was "always smiling and vivacious, a good skier and enthusiastic huntress, riding out with the Fife Foxhounds". She had done the London Season before returning north to curtsey at the Palace of Holyroodhouse.
The Scottish Season spanned August and September. For debs, Scotland was the last stop, "the absolutely final fling". So the very last curtseys to the Queen were made in Edinburgh at a ceremony in the Throne Room at Holyroodhouse on 3 July. The occasion was different in that both presenters and presented made a curtsey. The mothers or female sponsors curtseyed first and then the daughters, "adding up to a grand total of 600 curtseys".
The final Scottish debutante to "pass the Presence" was Miss Fiona Macrae, who lived in Edinburgh and was presented by Mrs David MacIntyre. "There was a primitivism about the presentations at Holyroodhouse which made Buckingham Palace seem almost easygoing," MacCarthy says. The Scottish Season was very grand, with the Perth races and the eightsome reels; the Scottish debs "would stick together like jam". The 10th Duke of Atholl was the eligible bachelor high on the list of the mothers of Scottish debs.
As well as telling the stories of some of the debutantes, her book is a deeply personal memoir. A highly educated, serious-minded young woman, "a natural swot", who spent the long summer of 1958 disguising her intellectual interests - she went up to Oxford University immediately after the Season - in order to survive as a very reluctant debutante. She escaped to find her own working-class hero, David Mellor, the renowned designer and silversmith, with whom she fell in love when the Guardian sent her to interview him in Sheffield.
Ironically, as she delved deep into her own memories, her husband, now 75, was losing his to dementia. He is now being cared for in a nursing home in Sheffield, some ten miles away from the business he created that earned him the title "the king of cutlery".
Their 38-year-old designer son, Corin, runs the family firm from the acclaimed Round Building factory, designed by architect Sir Michael Hopkins, behind which MacCarthy now lives with her fat cat Sophie, in the spacious home she and Mellor made during more than 40 "very happy, very stimulating years together. We travelled a lot; we talked a lot, and we've had the most wonderful life."
"David's illness is desperately sad," she says, adding that her husband was much missed on a recent September weekend, when she and her 36-year-old graphic designer daughter Clare, Corin, his photographer wife Helen and their son Hector, two, and numerous friends, attended the opening of a new museum, also designed by Hopkins, dedicated to Mellor's work and the astonishing range of his designs - everything from British traffic lights to award-winning cutlery. His name will live on, MacCarthy points out, since it's stamped into cutlery, made from local Sheffield steel, used in households and restaurants all over the world.
FIONA MacCARTHY came from new money. Her soldier father, Gerald MacCarthy, was killed in 1943, leaving her mother, the daughter of a French diplomat, Baron de Belabre, and his wife, Agnes McAlpine, granddaughter of Sir Robert McAlpine ("Concrete Bob"), to bring up her two daughters - Fiona and younger sister Karin.
"Neither by birth nor fortune (for in spite of the McAlpines, my mother was hard-up) was I up there with the grandest of debs," says MacCarthy. Her coming-out dance was held at the Dorchester, the hotel built by her great-grandfather's firm - "our own peculiar approximation of a London stately home".
Like Kay Thompson's Eloise at the Plaza, MacCarthy grew up as a hotel child. Her eccentric grandmother, Toto, lived there. And always in the background of "our lives at the Dorchester" loomed the clan McAlpine, the cohort of descendants of Sir Robert, solid in its maleness and denigrating to its females.
"It has always been mysterious to me why, with all the McAlpine millions, my mother had so little disposable income," she writes. Her mother was not even offered a discount for her daughter's dance, which she shared with another debutante, Jennifer Burness. So tormented did MacCarthy's mother become about not being able to pay the Dorchester account, she decided she must sell some of her jewellery. Her diamond clips were sacrificed.
MacCarthy found the whole episode desperately worrying. She remembers her dance well, "because it was a coming together, in that familiar setting, of my childhood past and an already fleeting present of myself as debutante". There was a fortune teller in a booth and every deb was told she would be married within the next two years. MacCarthy wore a strapless, dark-lilac satin dress with a harem skirt, which looked "particularly incongruous when worn with long white gloves".
So many memories, she says, explaining that in that time a certain sexual and social overlapping was already beginning. "What would become a lethal combination of snobbery and sleaze was already visible during the Season of 1958," she writes. So it was that one night after a dance she found herself in a lavish, rather flouncy flat off Shepherd's Market in London's Mayfair. She had gone there with Giles Havergal, one of her favourite dance partners, who later became director of Glasgow's Citizens Theatre.
"Giles was then a Guards officer at Caterham. He had driven up with the affably roguish Nicky Simunek, who was not an officer, and who was defintely not safe in taxis - unlike Giles," she says. There were about a dozen people at the party, lolling on sofas, entwined with each other, drinking lots of vodka. It was a night of many mysteries. Nominally in charge of proceedings were two Piccadilly tarts. Bedroom doors opened and closed. Shadowy half-dressed people came and went.
If this was an orgy, it seemed a little joyless and to MacCarthy's relief no-one invited her to join it. "I sat apart from the action, the impregnable virgin, like the figure of virtue in a medieval tapestry," she says. "Giles has only the faintest memories of the evening, although I recall it clearly. We've laughed about it so much since."
Oddly, she says, she befriended no other debs. Her longest lasting friendships have been with two gay men - "real debs' delights" - one of whom is Havergal. "Now what does that tell you about the Season," she says, artfully raising an eyebrow. "Everything."
• Last Curtsey: The End of the Debutantes by Fiona MacCarthy is published by Faber & Faber, priced 20.