Gangs of London features a wild mix of interweaving stories – blending trust, deceit, violence, betrayal and love into one captivating world.

Pete McKenna, who previously worked on shows including Kin, Hidden Assets and Red Rock, takes over the reins of the story for season 3, taking the story so far and putting his own artistic spin on what happens next.

The result is the most highly anticipated season of Gangs of London yet, with some brutal moves by the gangsters as their quest for power and domination of London continues. Working alongside Kim Hong-Sun, the show’s new director, it was up to McKenna to bring this story to life, interweaving everything we think we know into something even bigger than even the Wallace Organisation could imagine.

Speaking ahead of the series launch, Pete talks about how he planned out the latest episodes, how he juggled so many storylines at once, and how he built some truly killer action sequences.

I had just finished on a show called Kin, which was also in the world of gangsters and crime for AMC, one of the partners on Gangs of London. I got a call from AMC who said, ‘Look, I might have a really exciting proposition for you.’ I had no idea what it was going to be. He mentioned Gangs of London; I was a fan and I jumped at the opportunity.

At the start of creating this season, we really wanted to look at families, and what we did in a way was bring the family units back together. That was our starting point, but I often find with writing in general that you start with a theme at the very beginning, write the show and then discover you've written something else entirely. What I think becomes the theme is the price you pay in this world for this life. Everybody suffers.

There was a few, and sometimes they're not the ones you think. I really enjoyed writing for Billy this season. He's a really complex, tortured character who still feels trapped in the world he's in. He’s both quite cruel and good at being a gangster, while also being filled with self-loathing. That's really rich territory.

I always like writing for Lale. A strong female character in the male world; kickass, but also emotional. Some of her episodes this year are really strong. I also really like Marian. I love matriarchs, and the idea of a gangster wife taking over as the gangster. There’s something interesting about that, and Michelle gives such a good performance as Marian.

Zeek’s story is revealed slowly. We wanted the viewers to spend the first half of the series going, ‘Who is this guy? What's his agenda? What's really going on?’ Then the further down the series you go, the more it gets revealed, up until the very end. He’s a very elusive character, who's charismatic and has a big future in Gangs of London.

He's great fun, kind of unpredictable. He's a little bit uncouth, but also very useful. With the new characters, we tried to introduce them in a slow way, and it's the same with Cornelius. He gets a very good introduction at the funfair. When you meet him, at first you don't know who this guy is or what his links are. Then you get to see him across the series.

When we looked at the show in the last two series, what we felt had drifted out of the show a little was this sense of the world of London. So the businessmen, the politicians, the criminals rubbing shoulders together and kind of coexisting. That was part of the original DNA of the show, and we wanted to make sure we had that. Introducing Simone as the mayor of London, we get a sense of how politics, criminality and business all exist together. She's a really strong character. We’ve set up a backstory for her which we hope to play out in the future. In some ways, she’s a nemesis for the gangs at the beginning, but then it begins to change. She makes very unexpected decisions. We wanted to create a political character that wasn't the standard politician.

When you come into an existing show in my position, you want to both do justice to the characters who are already there and make your own stamp on it. What made it easy for me to do is I had been a fan of the show and loved the characters, so I was itching to get writing for them. It was a real, real pleasure. I'm really excited for the viewers to see what we've done, but when you come into a show loving the show, it’s easy to write for.

In the writers’ room at the beginning of the season there was myself, all the writers, executive producer Vikki Tennant, who’d worked on the show’s previous seasons and quite ostensibly across the scripts, the editorial team of Kathleen and a trainee. We all gathered there for about three weeks.

Myself, the editorial team and Vikki had worked a week or two before, saying ‘these are the things we want to do, these are the storylines’, some dictated by the end of last series, where you've left them or where you're picking up the story. We had ideas of characters we liked and those we wanted to explore in more detail in storylines that interested us. I felt some of the family units had been kind of fractured. Family is a really rich ground for exploring emotions, and as long as you have families together, you've loads and loads of material. So that was one of the things.

The editorial department keeps it all together, dealing with all the writers, making sure continuity is adhered to, reading everybody's scripts and making sure it feels like one story and not like there's lots of different people and voices in there. They're amazing.

Gangs isn't an easy show to write. It's a very particular style; a heightened high-octane world. But we really wanted to add a bit more emotional truthfulness this year, so marrying all those things into one show is tricky. We brought so many writers this year who did a brilliant job and captured the voice.

It takes a village. I always feel that about television, it's such an incredibly collaborative process. You write the scripts, hand it over to all these people who are brilliant at their jobs, and they begin to make their mark on the show. Key people we would work with are the directors, but particularly Hong-Sun. We’d have conversations, tonal meetings and talk about our intentions. Hong-Sun was directing for the first time in a language that was not his first language, and he'd worked in film, but never in TV before. It's a different process. What he did and achieved was incredible.

The script department would liaise with a lot of the departments, like stunts and production design whenever their work and our stories intersected. It's very important for us, we feel like we're creating the stories, but when the scripts go out into the world a little bit, you have to protect them because things can get lost. So the script department protects the scripts and makes sure intentions of the scripts are being relayed, but we're also open to collaboration.

When I discussed with the producers about coming on, the thing I found most daunting as a writer was the action. The rest you do all the time; characters, storylines – that's normal. It was the action where I was thinking, ‘my God, how am I going to write this?’ It's just so amazing what they do. By the end I really loved writing the action sequences. I tried to write them as I would imagine they were and root the action in emotional and personal stakes for the characters. But once you do that and you set down what you want, especially on this show, you hand it over, then you hand it to the stunt team and the director, and they come back and ask questions. If it doesn't impact the story, they'll invariably make it better and bring their own expertise. I've written stunt sequences before, but not on this scale.

A real challenge is to get the balance right. People come to Gangs of London for the action, that's what I felt when I watched Gangs of London as a viewer. It was unique as a British show, and felt like you’re watching a movie every week, epic in its ambition and what it achieved. But people also like to feel things, if it’s action without an emotional anchor, it's like watching a video game, and I don't think that really works either. So the challenge is to create characters that are real, truthful, emotional stories and within that world find places and find events that allow us to create the action the viewers want. When you get the balance of action, high stakes and emotional authenticity, the show really, really works.

I'm not very young, and I've been writing for a while, but it never, ever gets old, writing something, creating a script, and then seeing what you've written being performed, directed and come to life on screen. There's a lot of rejection, a lot of disappointment, and it's often quite lonely as a writer, but it's these moments that make it worthwhile. When you see the stuff you've written on television, see what people do, how actors and the heads of department and directors bring your work to life and elevate it, it's the best feeling.

One of the biggest challenges was how many characters there are. It's a very big ensemble cast – how do you give all of these characters stories that feel meaty and exciting enough, but also keep the show focused on a central storyline? Servicing such a great cast of actors was the hardest thing. It is a massive world. To give them all storylines, you're just cutting in and giving them quite superficial stories. If you want to give them proper stories, you need to spend time with them, but that always comes at the expense of other characters.

In general, not just in Gangs of London, you have to be very careful with flashbacks because when they don't work or not at their best, they kill the momentum and slow the story down. The flashbacks we've written are at the very beginning of the episodes when they appear, almost siloed away, so when we hit the ground running the story plays out in a present tense pace. The one exception is episode five, which cuts back and forward, telling Lale’s story in two different times. I think that works really well.