Former Call the Midwife star Olly Rix will debut in tonight’s episode of Casualty as the complex Flynn Byron.

As the medical drama’s latest boxset – titled Internal Affairs – kicks off, we will be introduced to Flynn and his complicated home life.

Complicated because we quickly learn that while the character has children and is in a relationship, he is also keeping a secret – he’s been having an affair.

Just recently I sat down with Olly Rix to talk about Flynn’s arrival to the Holby ED, and noted how this new face shares some similarities to Bones, another troubled and layered character he played in BBC One’s Our Girl.

‘He comes from a very specific world. On paper, at least, there’s something of an overlap with Our Girl because he’s come from a military background, a special forces background. But of course this isn’t a show about the armed services, it’s a show about the medical profession and the NHS’, Olly said.

‘What was so interesting with Flynn was to situate him in that world to begin with, so that when he comes into that civilian world and that NHS context he has a really different tempo. His metronome is different from other people’s, quite noticeably.’

As the chat starts to get underway, I can already tell how invested Olly is in the character.

‘Initially I talked to the exec producer about his military background and I suggested the special forces because it just accentuated the difference even more than if he was regular military’, he told me.

‘He’s hyper-focused, hyper-independent, an extremely capable and exacting individual and he brings that to bear on everything and everyone around him, including himself. It’s quite an interesting jumping-off point.’

He added: ‘I actually got to spend some time with current members of the UK special forces, a few of whom were literally about to go on tour as Flynn is in the story. They were very generous with their time and I asked them some very personal questions.

‘I talked to them about compartmentalising their lives and sort of having a switch inside them that they can flip as and when they need to, to go and do some very, very extreme things and co-exist in a normal civilian context with families and wives and kids.

‘It’s something we definitely tried to tease out in that opening episode. We didn’t want Flynn to come from a background that suggested he wasn’t rooted in the civilian world. He is. He’s just trying to negotiate that balance. He doesn’t always get it right and a lot of his arc is having to learn how to do that in a different and extreme way. It’s not something he’s had to do before.’

Moments after Flynn’s meeting with secret lover Amber, the two are involved in a major RTC. As paramedics Iain (Michael Stevenson), Teddy (Milo Clarke) and Jacob (Charles Venn) arrive, the perspective of the episode changes as we watch the chaos unfold effectively through Flynn’s eyes.

Olly explained: ‘I was very fortunate because I had an amazing director, George Siougas, who directed that first episode and we had a wonderful relationship and I really love the guy. I sort of led it. I had to, because I was literally built into the camera rig so I was operating the camera in any POV shots – I’m doing it, it’s not a camera man doing it.

‘It was a really unique experience, I’ve never done anything like that before. It meant I had a huge amount of responsibility on my shoulders because I was part-directing the episode as well.

‘We did everything we could to contrive a situation where it just happened quite naturally, so I wasn’t having to have the director run on to the floor and say “Watch that bit” or “Face that way.” There was no real technicality about it, it was a very free and organic experience.’

Towards the end of the episode, it’s Stevie (Elinor Lawless) who is the first to learn Flynn is the ED’s new Clinical Lead.

And as Olly revealed, Flynn makes quite the impact on the staff as he gets settled into the role.

‘I think in a way he sort of clashes with everybody, because it’s his way or no way. Flynn likes things done how he wants them done. It’s not to say that he doesn’t have respect for the other professionals he’s surrounded by, because he really does. He has massive professional respect for Stevie, massive professional respect for Dylan.’

‘He has a very different relationship with Stevie than he does with Dylan but it’s not a question of whether he respects them as doctors or clinicians – he just wants it done his way. So if he comes up against what he sees as the more pragmatic, bookish approach of Dylan, he doesn’t have time for that. He wants real world quick applications, quick solutions.

‘Dylan has had time and experience within this NHS context that Flynn hasn’t. So it’s never about one character being right and the other being wrong, it’s a constant push and pull of who’s learning what from who at any given moment.’

‘He’s very capable of making very quick decisions, and once he’s made a decision he wants it implemented fast and be efficiently executed. That runs into some tension and conflict along the way because he doesn’t have much time for things he thinks aren’t a good use of time.’

Pondering over Flynn’s arc throughout the next 12 episodes, Olly told me he believes fans of the BBC One show will eventually come to love the new doctor.

‘I’ve loved him from the off. Even in the first episode, even though he’s badly behaved and he’s done clearly morally questionable things, he’s such a decent person. I think the key to Flynn is understanding he’s just a product of an environment – a very specific, high tempo, high pressured environment that doesn’t really take prisoners.

‘So it’s moulded a person who’s sometimes harsh, very exacting, who holds himself and others to almost impossibly high standards, all of which seem unfair.

‘But I think you really see Flynn become a very indispensable part of this world and a very loved and relied-upon keystone to this department and this hospital. He doesn’t allow his staff to be pushed around, he doesn’t let anyone take any liberties with them or bully them. He’s often fighting the bureaucracy, the red tape, whatever, for the sake of the staff that he looks after.’

He added: ‘He’s a taskmaster, but at the same time he’s got an amazing heart and we see that throughout the series. When you first see that side of Flynn and see him soften is with his bedside manner and his manner with patients.