Jenna Coleman has said it was “absolutely necessary” to keep things light between scenes while filming emotionally heavy new drama series The Cry.

Coleman plays a new mother called Joanna who is grappling with a psychological breakdown and post-natal depression, and then has to cope with the abduction of her baby after travelling to Australia.

The Doctor Who and Victoria star said the role is possibly the most challenging of her career, and that working with babies on-set has been “lovely” but “emotional”.

Coleman said: “What’s been really remarkable about filming – given the emotional marathon for everyone involved – is how light it has been in between scenes.

“It’s been absolutely necessary. We just had a real laugh.”

On the difficulties she faced, Coleman said: “The psychological thriller aspect of how much you give to the audience has been really challenging – probably more than any other role before.

“You are constantly living within a double-bluff. You’re playing the truth of the scene but also thinking about how much you want to give to the audience each moment to keep the mystery and to keep drawing on the strings.

“You’re living constantly within a vortex, that’s what we kept calling it on set. It’s a double bubble.”

She said she will miss working with twin babies who portray her on-screen son Noah, adding: “It’s been lovely. But it’s been emotional.

“We’ve been unbelievably lucky. The babies were like these magic, genius actor babies who seemed to know what the word ‘action’ means and what the scene required! They’ve made my job very easy. Genius babies.”

The story sees Joanna and her husband Alistair, played by Ewen Leslie, travel to Australia from Scotland to see Alistair’s mother and also to fight for custody of his teenage daughter from a previous marriage.

Jenna Coleman and Ewen Leslie in The Cry
Jenna Coleman and Ewen Leslie in The Cry (Synchronicity Films Ltd/Lachlan Moore)

However, things go awry when their baby is abducted, and the young couple are thrust into the public spotlight in the series, adapted for TV by Jacquelin Perske from Helen FitzGerald’s novel.

Top Of The Lake star Leslie said his character, an adviser for a political party in Scotland, is “someone who likes to be in control” and starts to unravel throughout the series.

He added: “He is a tricky character. I imagine he will be a tricky character for the audience. He’s a tricky character to play because he’s not very sympathetic.”

Coleman said Leslie was “extremely clever at switching” in-between scenes.

“In some ways, Alistair is charming and generous, you could see him as the ideal partner in many ways, but yet you could also see Alistair as controlling, manipulative,” she added.

“It takes a skilled performance to have all those aspects of that character and be delivering that very delicately.”

The Cry will air at 9pm on Sunday September 30 on BBC One.