A former lady-in-waiting to Princess Margaret tells Sarah Ell why she decided to write a no-holds-barred memoir

Despite the times we live in, the British aristocracy still has pulling power. The Downton Abbey movie, revolving around a royal visit to the fictional pile, has made more than US$135 million at the box office, while the third series of award-winning Netflix drama The Crown goes live in November.

It was the production of this third series, covering the years 1964 to 1977, that spurred one of the minor players in the real-life royal saga to sit down and write her life story. Lady Anne Glenconner, now 87, has produced a memoir, called Lady in Waiting, about her position at the side of one of the black sheep of the royal family — Queen Elizabeth's younger sister, Princess Margaret.

In The Crown, British actress Nancy Carroll plays Glenconner while Helena Bonham Carter takes over the role of Margaret. Alongside other storylines, the series will portray the breakdown of Margaret's marriage to Lord Snowdon (a commoner born Antony Armstrong-Jones, who Glenconner's aristocratic father dismissively called "Tony Snapshot") and the affair with the dashing Roddy Llewellyn, a minor aristocrat 17 years Margaret's junior.

The real-life Lady Glenconner (nee Lady Anne Coke) played a major part in these events, offering Margaret sanctuary on her family's Caribbean island of Mustique during her marriage breakdown and also unintentionally introducing the princess to Llewellyn at a house party at their Scottish mansion, Glen. Margaret went with Glenconner's husband, Colin Tennant, to pick up their last-minute guest from the station and the princess and Llewellyn returned hours later, "more or less holding hands".

But Glenconner had never thought about recording her version of events — which spans a sweep of 20th century history from World War II through to the Queen's coronation and into the decadence of the 70s and 80s party scene — until Carroll and Bonham Carter came to visit her to study for their roles.

"I was very pleased [to meet Carroll] because she is rather pretty," Glenconner says, but adds that it was unnerving, "because when I talked to her I kept thinking, 'She's listening to me talk and looking at the way I walk.' It was rather surreal. It made me think how lovely it was that Princess Margaret and I were going to be together again and gave me the idea of writing a book about it."

Three months later, she'd done it, producing a refreshingly honest look not only at life in the royal circle but also the double-edged sword wielded by great wealth and privilege: on one side the grand houses and lavish parties; on the other some outlandish and downright barmy behaviour, paired with personal tragedy on a grand scale.

Tennant, the third Baron Glenconner, could most charitably be described as eccentric, prone to fits of violent rage and anxiety attacks which would see him curl up a ball, scream or throw things. Of their three sons, two died as young men — one from hepatitis C contracted through drug use and the other of Aids — and the third suffered brain damage following a motorbike accident. Then, to top it all off, she and family were disinherited by Tennant when he died in 2010, in favour of one of his Caribbean employees.

"It wasn't perhaps the book that people thought I might write," she says. "I think some people expected some lavender-infused little memoir but I decided I wasn't going to write a book like that. I was going to write a book about what happened to me and how I felt about it and if people don't like that, that's too bad."

Lady Anne Glenconner, now 87, has written a memoir about her position as lady in waiting to Princess Margaret. Photo / Hal Shinnie

Lady in Waiting throws a much more personal light than usual on the royals. Glenconner's comfort with the monarchy came from growing up with them. Her father's estate at Holkham in Norfolk was just 16km from the Sandringham estate and the Coke (pronounced Cook) family would shoot and socialise with the royals. (Glenconner writes, "Queen Mary had once rung my great-grandmother, suggesting she come over with the king, only for my great-grandfather to be heard bellowing, 'Come over? Good God, no! We don't want to encourage them!'")

"When we were children, we used to play a lot together. Princess Margaret was near in age to me — the Queen is a bit older — so we just always knew them," Glenconner says.

This family connection led to Glenconner being asked to be a maid of honour at Queen Elizabeth's coronation in 1953, one of the first major events of the television age. Around the world, more than 200 million people watched the three-hour ceremony — a fact Glenconner was acutely aware of when she felt she was going to faint during the ceremonial anointment of the new Queen. Fortunately, she was standing next to the delightfully named Gentleman Usher of the Black Rod.

"Black Rod saved the day — he was a splendid man, dressed entirely in black velvet holding something which looked like a billiard cue. I remember thinking, 'I absolutely can't faint in front of billions of people' but when I started to sway backwards and forwards, he just put his arm out and kind of pinned me to a pillar."

In 1971, Margaret asked Glenconner if she was going to have any more children. "I said 'Absolutely not, I have three boys and twin girls and I think that's enough' and she then asked me if I would become one of her ladies-in-waiting."

The invitation came at a good time, Glenconner writes, because her husband "was going through a particularly difficult phase". (He'd recently been banned for life from British Airways, after throwing an enormous tantrum after not getting a first-class ticket on a transatlantic flight.)

With her children in the care of nanny Barbara Barnes, who would later look after princes William and Harry and with Colin spending more and more time on Mustique, Glenconner was free to accompany Margaret on her many official engagements in the UK and around the world. During time, the role blurred the line between friendship and duty.

"I think the thing was, she always chose friends to be her ladies-in-waiting," Glenconner says. "You spend a lot of time together and, at the end of the day, it's good to have a friend to laugh and talk with. However, when one was on duty, one's job was to be there for her if she needed anything. At lunch or dinner I'd always sit within eye contact of her, so if she wanted anything she would just look at me."

Glenconner describes the late princess as "extremely clever. She would have loved to have gone to university and felt that she wasn't well educated, unlike the Queen who had tutors from Oxford and Cambridge. But she was a very clever person, very well read."

Freed from royal protocol and the lenses of the press, the princess could also be informal. Tennant offered her a plot of land on Mustique as a wedding present and, during her marriage breakdown, she built a house there, Les Jolies Eaux, which became a welcome retreat.

"I used to swim for miles with her — she would do breaststroke and I would sort of swim along on my side, so I could talk to her," Glenconner says. "We had a lovely time together there."

Centre of attention with Rolling Stone Mick Jagger and actor Rupert Everett.

While there is more than enough royal detail in the book to satisfy the most ardent monarchists, perhaps more fascinating is when she writes about her own life. Born the daughter of the future 5th Earl of Leicester, Thomas Coke (her mother, born Lady Elizabeth Yorke, was also the daughter of an earl) she seemed destined for a life of royal service. Her father was equerry to the Duke of York, who became King George VI in 1937, and her mother was appointed a Lady of the Bedchamber — a sort of uber-lady-in-waiting — to Queen Elizabeth when she was crowned in 1953.

Glenconner also has a Kiwi connection - her maternal grandmother, Ellen Russell, was born here, the daughter of colonial lawyer James Russell. Russell arrived in the new colony with his parents in 1840, trained as a lawyer and established the firm that would eventually become Russell McVeagh.

Ellen and her two sisters were sent back to the UK to find husbands; Ellen landed the 8th Earl of Hardwicke (though later divorced him because of "cruelty") and during World War I worked with Sir Thomas MacKenzie, the New Zealand High Commissioner, to establish a hospital to treat New Zealand soldiers. Ellen was in charge of the entertainment committee and took recovering patients out on her husband's yacht.

Glenconner was brought up at Holkham Hall, a Palladian pile so vast that, according to her book, "the footmen would put raw eggs in a bain-marie and take them from the kitchen to the nursery; by the time they arrived, the eggs would be perfectly boiled." Her father wanted her to marry one of his friends, Lord Stair, but instead she chose Tennant, whom she describes as "tall and terribly handsome" but also with "a very unfortunate temper". Glenconner didn't find out until years later that her friend Princess Margaret had written to her mother warning her off Tennant but, typically, both women had decided to "settle on acceptance rather than intervene too much".

Marriage to Tennant was tumultuous and Glenconner doesn't spare on details. She describes with some relish her husband's "surprise" idea of taking her to watch two strangers have sex in a dirty hotel, on the second day of their six-month honeymoon. "It had all started in Paris, a place I have never quite been able to relax in since. The next time Colin and I went, he took me to a stage show of a man making love to a donkey," she writes dryly.

In 1958, while visiting family properties in Trinidad, Tennant decided to buy Mustique, for £45,000. The island had no electricity or running water and was infested with the mosquitoes from which it got its name, but he was determined to develop it into a luxury private resort.

Roddy Llewellyn, Princess Margaret, Lady Anne and her son Charlie.

In the 1960s and 70s, the island would gain a reputation as a bolthole for the rich and famous. Glenconner writes of the spectacular parties that would be held there including Tennant's 50th birthday "golden ball". A week of festivities culminated in a massive party at which everything was spray-painted gold, including the beach, the grass and trees - and people.

"I was less thrilled because somebody had suggested that I should paint my face gold but it had the most terrible effect, highlighting every wrinkle and crease. I spent a lot of the party trying not to smile," Glenconner writes.

But in the midst of this gilded hedonism was also personal tragedy. In December 1986, just minutes before Tennant's 60th birthday "Peacock Ball" was about to kick off on Mustique, he told her their second son, Henry, had been diagnosed with HIV — then a new and frightening disease. She writes: "To be handed my son's death sentence while standing in a glittering dress welcoming lots of guests felt like some sort of obscure nightmare."

"When Henry got Aids it was terrifying because at that point no one really knew how you caught it," she says. "A lot of our friends suddenly didn't come to stay any more, but Princess Margaret always came and she brought [her children] Sarah and David to stay. She always went to hug Henry when she saw him. She then became patron of the Lighthouse, a place for young men who were dying of Aids. She wasn't touchy-feely but she'd come into the room and make them laugh. She came to Henry's funeral, too."

The Coke family crest is "an ostrich swallowing an iron horseshoe to symbolise our ability to digest anything" and Glenconner has certainly had plenty to digest. Yet she has emerged from her roller coaster of a life with her sense of self, poise — and humour — intact. She is warm and chatty, despite unself-consciously referring to herself as "one" throughout our interview. You get the impression that she must have been great company for the famously dour Margaret. In short, she sounds like a tremendously good sport.

By the time our conversation ends we are chatting about yachting — she sailed all her life, only giving up her dinghy for good at the age of 80 — and I promised to take her sailing if she ever comes to Auckland.

She is a firm believer of life being what you make it, her stoic attitude instilled in her by the strong women of her family.

"While in some ways I was very, very lucky, I was dealt a pretty awful hand in other ways, losing two sons and the other having such a terrible accident. But I always felt that God would never send me more than I could manage. I was brought up never to give in and to keep going; to make the best of what I had been given.

"Maybe that's the part of me that comes from New Zealand. It was quite a thing to emigrate in those days and you had to be a strong person to survive. That must be my New Zealand side."

Lady in Waiting by Anne Glenconner (Hachette, $50) is out on Tuesday, October 17.