As part of a series of dramas charting the lives of iconic British women, the actress Anne-Marie Duff depicts Fonteyn as she was when she met the Russian dancer, Rudolf Nureyev.
The legendary partnership they forged lasted nearly 20 years and propelled them to a level of celebrity not experienced before or since in the world of dance.
"The whole paparazzi issue for Rudi and Margot, I found it astonishing how huge they were - international superstars, in that field," says Anne-Marie. "If you ask people now who's a famous dancer they might come up with Darcy Bussell, and if they know anything about dance, Carlos Acosta - beyond that nothing. You can't imagine ballet having that sort of huge influence. I just found it shocking."
The duo's electric performances created such a frenzy that 40 minute standing ovations weren't unknown.
But what made Fonteyn and Nureyev's relationship all the more tantalising was the fact he was 19 years her junior. When the couple met, Margot was 42, an age when many expected her to retire.
"Nureyev brought a new life, a new chapter, just at the point where she was having to slow down," says Anne-Marie. "She was beginning to find herself being overtaken by the younger ballerinas and in comes this Russian tornado who makes her 25 again. It is incredible."
For Anne-Marie who admits she was never "a ballet child", the research she undertook in preparation for the role opened up a whole new world.
"I had no idea what an incredibly huge icon Margot was, not just in terms of a creative icon, but she was also a style icon. I had no idea she was up there with Audrey Hepburn and Jackie Onassis in terms of that kind of image."
Fonteyn's dramatic private life also proved an enticing factor. "That's when it became really interesting," says the 39-year-old actress with girlish laughter.
"I love the idea of this seemingly perfect individual having this manic, chaotic existence at home which was driven by desires that have nothing to do with the stage."
In 1955, Margot had married the Panamanian diplomat Roberto 'Tito' Arias, with whom she had a tumultuous relationship and Fonteyn was aware of his numerous infidelities.
"Her choice of husband was curious and a risk," says Anne-Marie, referring to a man who was famously absent from many of Fonteyn's public performances.
"Tito wasn't available to her physically or emotionally in a way that could have made it easier. Perhaps she adored that, perhaps she loved the freedom of that and also the delicious agony of it, you don't know."
And then of course there was Nureyev. Such was their passion on stage that rumours abounded that the two were having an affair.
"It was no secret theirs was a passionate relationship," says Anne-Marie. "There was an enormous amount of chemistry on stage and in the rehearsal room. They laughed together all the time and he was such a presence within the rehearsal room, he made himself known very quickly, and people saw a change in her and in her dancing."
As for whether Anne-Marie believes they embarked on a physical affair, she pauses before saying, "The fact dancers spend so much time intimately entwined when they're dancing, I don't think it's such a great leap to believe they might have had a relationship. She did fall in love with him, she said she fell in love with him."
It's little surprise the matter of whether they were lovers remains a mystery. Even now 18 years after Fonteyn's death, many of Fonteyn's contemporaries remain tight-lipped. "I met lots of people that knew her, older dancers, choreographers," says Anne-Marie. "It was tricky sometimes because they were terribly protective of her." They did divulge little nuances that helped Anne-Marie to understand Margot's character though.
"It was quite nice because without people realising they let you know the silly things about her and that's always what you're interested in as an actor. Her perfume, a silly laugh, she was always rubbing her foot - things like that. Apparently she had a really girly giggle, she was a real laugher," she says.
In the flesh Anne-Marie may have the petite physique of a ballerina but that isn't enough to portray one of ballet's leading lights, so Anne-Marie and Michael [Hausman, who plays Nureyev] embarked on a period of intense training with dancers from the Royal Ballet.
"It was punishing and I felt like an absolute fool every day," says Anne-Marie laughing and cringing at the memory. "I sat in on classes, workshops and rehearsals and just watched dancers because they're just so different from actors - it's a completely different world."
But there was only so much Anne-Marie could learn in a few weeks. "Obviously we had to have doubles because as much as you can work on your upper body, there's no way you can make your legs look like they've had 20 years of dance training, it's impossible in six weeks! My objective was to be standing in a suit or sitting at a table and for people to think, 'Yes, she's a dancer' because carriage is everything for a dancer - they're so open and different. That was the priority."
It's this attention to detail that has marked Anne-Marie out as one of Britain's leading actresses. After coming to prominence as Fiona Gallagher in the Manchester-based TV series, Shameless, a role for which she was twice BAFTA-nominated, she received a further nomination for her portrayal as Queen Elizabeth I in The Virgin Queen. Next she appears in the artist Sam Taylor Wood's directorial film debut, Nowhere Boy, as John Lennon's mother Julia.
"I thought the script was like nothing I've read before and I was really desperate to do it," says Anne Marie. "I had that response you have when you first start acting and auditioning for things and you think, 'Please let me get this job!'"
Extra time - Anne-Marie Duff
She was born on 8 October 1970 in London.
She met her husband, fellow actor James McAvoy, on the set of Shameless in 2004 and they got married in 2006.
She studied at The Drama Centre in London and was nominated for a Laurence Olivier Theatre Award in 2000 for her appearance in Collected Stories.
She's perplexed by young Hollywood actors who command film sets. "My [theatre] background is more about the director being in control. It's all about yielding."
Whenever she's feeling stressed, she like to bake cakes as she finds it therapeutic.
