Considered one of the best dancers of all time, Dame Margot Fonteyn was one of only two British ballet dancers to ever receive the accolade of prima ballerina assoluta and was globally adored during a career that spanned 45 years.

As part of a series of dramas charting the lives of iconic British women, the actress Anne-Marie Duff, who's probably best known in this country for her role in The Magdalene Sisters, 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 Darcey Bussell, and if they know anything about dance, Carlos Acosta -- beyond that nothing. You can't imagine ballet having that sort of huge influence."

The duo's electric performances created such a frenzy that 40-minute standing ovations weren't unknown.

Tantalising

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, and expected by many 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, the research she undertook in preparation for her role in Margot opened up a whole new world -- and she was intrigued by Fonteyn's dramatic private life.

"That's when it became really interesting," says the 39-year-old actress with girlish laughter.

In 1955, Margot had married the unfaithful Panamanian diplomat Roberto 'Tito' Arias, with whom she had a tumultuous relationship.

And then, of course, there was Nureyev. Such was their passion on stage that rumours abounded that the two were having an affair -- but the truth remains a mystery.

"There was an enormous amount of chemistry on stage and in the rehearsal room," says Anne-Marie. "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."

To help her portray one of ballet's leading lights, Anne-Marie 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," she says, 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."

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!"

Desperate

It's this attention to detail that has marked her out as one of Britain's leading actresses. After coming to prominence as Fiona Gallagher in the TV comedy drama Shameless, she was feted for her portrayal as Queen Elizabeth I in The Virgin Queen. Next she appears in the film 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. I had that response you have when you first start acting and you think, 'Please let me get this job!"'

Margot airs on November 30 on BBC Four at 9pm