When Olly Rix sits down with What To Watch to discuss his much-anticipated Casualty debut he’s in a state of disbelief that army medic Flynn Byron is about to make his on-screen appearance in a special, introductory episode this week.

“It’s funny, I’ve had nine months where I’ve been so busy filming in Cardiff, I’d almost forgotten this was going out on TV,” smiles the former Call the Midwife star. “It’s been such great fun, so it’s nice to finally talk about it.”

Olly’s much-anticipated debut in the BBC1 medical drama this week coincides with the launch of the show’s latest mini-series, the 12-part story Internal Affairs. The plot sees Flynn preparing for a dangerous mission abroad when destiny diverts him to Holby City Hospital.

Here Olly discusses the life-changing events that eventually lead to Flynn’s appointment as the ED’s newest clinical lead…

Olly Rix — an exclusive Casualty interview

Congratulations on landing the role of Flynn, Olly. How did it come about?

“I was invited to lunch with Casualty’s executive producer and we had a lovely collaborative discussion about the character. Afterwards I sat down and watched recently aired episodes to have an idea of the current iteration of the show, and I was taken aback by the tone, the writing, how well it’s shot and the cast, so it was an easy decision!”

What’s going on in Flynn’s life when we first meet him?

“You see him days before he’s due to be deployed and, psychologically, he’s in a very specific space of being battle-ready and capable of extreme compartmentalisation. This deeply affects his relationships with his neglected wife Claire [played by Doctor’s Elisabeth Hopper] and children Poppy and Millie [played by Lola Grace Maurice and Elsie Antonia Maurice].”

Things take a dramatic turn when Flynn’s colleague and affair partner, Captain Amber Mitchell (The Way’s Sophie Melville) is involved in a road-traffic collision, which begins a chain of events that see Flynn fighting for his life. What more can you reveal?

“When the collision takes place the episode switches from conventional filming to point-of-view filming and you get to see who Flynn really is, from the way he reels off information to the ambulance call operator, to doing multiple things at the crash site in a calm, collected way. Even on death’s door, covered in blood and an absolute mess, he’s making clinical assessments about what’s going on around him.”

What an exciting introduction!

“It’s an amazing starting point for a new character – he crashes into this well-known world from a very different perspective, and you get a unique insight into his interior self and inner monologue and how he copes with being a patient. To film these scenes I was built into a rig and operated the camera – I’d never done anything like it before!”

This isn’t your first time portraying a character with a military connection, as you also starred in BBC1’s Our Girl. What research did you do for your Casualty role?

“I spoke with some incredibly generous, actively-serving Special Forces members about leaving their families, near death experiences and how physically strong you have to be to move casualties on a battlefield while sustaining enemy fire, or in a hostage situation, or trying to stem bleeding while being thrown around in the back of a helicopter. They were great and did a lot of physical training and simulations with me to get a sense of how noisy, distracting and overwhelming it is.”

Does Flynn’s arrival herald a change in tone for the show?

“I have to be careful about spoilers, but there’s definitely been some reinvention here. Tonally there’s a level of grit and realism across this miniseries that we carry forward very deliberately. Flynn’s a great way to do that, because he’s from a world that’s gritty and dark and allows us to introduce those aspects of the NHS at the same time.”

The next episode sees Flynn become Holby ED’s new clinical lead. What’s he like in the role?

“Initially, he’s an extremely flinty and exacting boss, so, even though he respects his colleagues, his approach leads to interesting conflicts. He has to learn he’s in a civilian context now and not barking orders to soldiers. You will see a bit of delight from other characters when he makes strong decisions that don’t work out!”

Is there anyone he particularly clashes with?

“He has a bit of conflict with everybody, but without giving too much away, Flynn and his father-in-law – surgeon Russell Whitelaw, played by Robert Bathurst – loathe each other! There’s also a fiery back and forth between Flynn and consultant Stevie Nash [Elinor Lawless]. They knew each other when they were medics at university, so there’s history there. She brings out his roguish, boyishness!”

The Casualty set is incredibly detailed. How are you finding working on it?

“Yes, it’s extraordinary and it really feels as though you’re in a hospital! With all the gloves, hand sanitiser and everything else, it even smells like a hospital. Even the prosthetics feel as though they’re real – fortunately I’m not squeamish!”

The Casualty cast are famously very welcoming. Did you know anyone before you started working on the show?

“I didn’t know anybody when I joined, but I’ve made good friends. It’s a wonderful show to be part of and Flynn is about to go on a big, exciting journey.”