Vanessa Kirby would have felt “daunted” if she’d starred in later series of ‘The Crown’

She told Sunday Times Culture magazine: “I didn’t know anything about Princess Margaret.

“And from the 1950s all you could find were little clips of her opening things, like boats.

“I had to find moments where her mic was left on and she said a withering remark.

“I’d have felt daunted if it was closer to today. It’s more current. More controversial.”

Meanwhile, in her next movie, ‘Pieces of a Woman’, Vanessa portrays Martha, who is left grief stricken after her baby is stillborn, and she felt daunted by her first scenes, which depicted her giving birth.

Because she’s never had children of her own, the actress contacted London’s Whittington Hospital and asked if she could observe a birth – and was stunned when an expectant parent agreed.

She said: “I walked in in my scrubs. We had asked permission and unbelievably she said yes. Not sure I would. Some random actress in there…

“Anyway I sat next to her on the bed and vaguely waved. I was in awe. Her mother was there too. I hardly breathed for six hours.”

Asked if she offered encouragement, she exclaimed: “No! Can you imagine? ‘Go on, girl!’ No, I was silent. It was a greater achievement than I’ve seen anybody do. There were forceps.

“At one point she looked at me. Halfway through a difficult contraction. I blew her a kiss. Why? So embarrassing.”

Although she didn’t know the family, Vanessa found the experience very moving.

She continued: “And when he was actually born the nurses brought me round to see him come out. I was crying my eyes out.

“All colour came back to the mother. It was holy.

“And then I was introduced, and they went, ‘Oh God, Princess Margaret!’”