As Call the Midwife newcomer Nancy Corrigan delivered her first baby tonight, viewers might have put her apparent expertise down to Megan Cusack’s great acting.

But Megan, 24, has revealed she got tips from a real midwife – her maternal grandmother Margaret Harris.

Despite her family tree looking like a Who’s Who of acting – with aunts Niamh, Sinead, Sorcha and Catherine, not to mention uncle Jeremy Irons – it’s her grandmother she is most keen to impress with her first television role.

Megan said: “My grandma’s a massive fan of Call the Midwife. She was just saying how well they capture it all in the show. She was like, ‘Yeah, absolutely. I remember things like that’.”

Sister Monica Joan in Call the Midwife
Sister Monica Joan

Megan said it had been useful to have nursing genes alongside the famous Cusack ones when she landed the role.

She’s now looking forward to getting back to her native Ireland and hearing what her Granny has to say about Nancy.

Tonight the show’s 8 million fans saw an expectant mum spurn Nancy because of her overbearing bedside manner and forthright way of speaking.

Call the Midwife
Nancy delivered her first baby in tonight's show

But later she had to rely on the young nurse after the baby started to arrive and no one else was available to help.

Although Megan says she’d be no good as a real midwife because she is “not good in high-pressure situations”, the actress says there are lots of similarities between herself and her character.

Megan said of Nancy, who arrived last night as part of a training programme: “She’s just a bit dizzy, isn’t she?

Megan Cusack as Nancy in Call the Midwife
Megan says she would be no good as a real-life midwife

“She’s away with the fairies a lot of the time, I think. And I would lose my head if it wasn’t screwed on.”

Of filming the fraught birth scene, she said: “I’m not going to lie, it was nerve-wracking. But when it comes down to it, Nancy can handle the situation.”

Megan also gave credit to long-serving co-star Judy Parfitt, who plays elderly nun Sister Monica Joan, for guiding her through her Nonnatus House debut.

She said: “It was nice having her give me a little bit of advice as we were filming because you don’t have too long to overthink it. You just go, ‘OK, I’ll do that. Let’s give that a go’.”