Rosie Day in When It Happens to You at Park Theatre

"Luckily Amanda and I have known each other for years, this is our fourth time working together and it's just a joy," says Day of her fellow North Londoner.

"She's the kindest woman, with a heart of gold. For such a heavy subject matter we have been laughing so much - I can't think of a better person to play this role, we have formed a really strong relationship and hopefully that shows on stage - given the subject, you have to find laughter in rehearsals."

Tawni O'Dell's powerful 'theatrical memoir' is based on her experience of the shockwaves of trauma following her daughter's brutal rape by a stranger who broke into her home.

Rosie Day and Amanda Abbington in rehearsal for When It Happens To You (Image: Mark Douet)

Pertinent to the issues raised recently by Abbington about her stint on Strictly Come Dancing, Day adds: "We feel very safe and supported in handling this subject matter.

"But there are moments when you step out of the rehearsal room, take a breath and go back in again."

When It Happens To You  at Park Theatre is a tense 85 minute thriller, as Abbington's Tara blames herself for not protecting her daughter, and Day's Esme turns her shame and anger on her loved ones.

Abbington has said: "I immediately read it in one sitting – I couldn’t put it down. The story is important and necessary, and the characters are nuanced, complex and completely relatable. The character of Tara is a gift of a role for any actor, and I know Jez Bond will direct the piece with the care and sensitivity it deserves."

Day says: "It's a rollercoaster that starts and does not stop. I have never read anything that looks at the effect (rape) has on a mum, a daughter, and a brother watching them fall apart. It's so real, so unflinching and honest, but also hopeful. It feels very vital."

Day whose acclaimed monologue Instructions For A Teenage Armageddon deals in part with non consensual sex, says: "I have lived experience of Esme myself, and when you try to talk about it or raise the conversation, people often shy away or pretend it doesn't happen as much as it does.

"The statistic is that one in four women are raped. That's reported, lots are not. There's a line in the play that if every woman who had been raped also lost a limb you would see it in society.

When It Happens To You runs at Park Theatre from July 31 until August 31 (Image: Mark Douet)

"I hope the play starts a dialogue about what happens afterwards, how it bleeds into your life."

Day has not only had therapy, but is training to be a therapist, and says "therapy saves lives and can rebuild a life."

But she observes that Esme initially tries to deal with it herself: "It festers in a way that slowly becomes quite mean and angry and she pushes everyone away. She's affected by how other people treat her when they try to molly coddle her, she doesn't want to be treated as a fragile doll."

Ultimately Tara and Esme "find their own path and different ways to slowly come together again and heal."

"At no point are we putting on a play about lives ruined forever," Day stresses. "I hope we empower the women and men in the room who have been raped that this does not define you. You can overcome this."

Day is relieved to be playing a grown up after "playing teenagers for about fifty years."

Her acting career started aged four in John Boorman's Hope and Glory and she graduated from a child actor on stage and screen to a string of teen roles including young Mary Hawkins in Outlander and Sarah Jessica Parker's daughter in the rom-com All Roads Lead to Rome.

"We were the only non Italian people on set and spent all our time together. For three months we were in each other's pockets and it was so much fun.

"She's so funny and iconic, there is absolutely nothing she doesn't know about filming."

Teenage Armageddon, which covers eating disorders, self-harming, toxic friendships and sibling bonds with a quirky humour, sprang from Day realising that teenagers are "so often written unrealistically, by people who were never were one".

"I was doing a play and wondered out lout why there are no one-girl plays.

"Teen girls are never given enough credit or a voice. So the director said 'go and write me one.' It started as a dare, I wrote it in my bedroom, and it's been the gift that keeps on giving."

When it played in the West End recently, one critic called it a cliche, with Day, now an ambassador for Teenage mental health charity Stem4, calling them out on X saying it was based on her own life.

"Sometimes a cliche is a cliche because these things do happen to teenage girls. It's why I write now, I love having the chance to tell stories. As a young woman growing up as an actor, I felt so powerless, at the behest of other people, acting wasn't doing anything for me for a while."

Now focusing on her writing, Day is adapting Teenage Armageddon for a BBC Three series Executive Produced by West Hampstead's own Emma Thompson. She's also writing a new play and a book I Think I Like Girls.

She says: "Emma Thompson is amazing, she came and saw me in Armageddon at Southwark, I walked out into the auditorium and forgot my first line because I saw her. She has been a massive advocate for the piece."

"I feel very lucky to get to sit in a coffee shop and write and earn a living."

But she was lured back to the stage at Park Theatre because she wants to do work that "fits in with what's important to me."

"With this, it's talking about trauma and how you survive it, having lived that myself, I wanted to do a piece that educates people who know people who have gone through it."

When It Happens to You runs at Park Theatre from July 31 to August 31.