How to Get Cast on ‘Slow Horses’

Based on Mick Herron’s “Slough House” book series, “Slow Horses” follows Jackson Lamb, who leads an MI5 unit for operatives who have failed a mission…but not bad enough to get fired. Lamb’s Slough House is staffed entirely with these disgraced agents, known as “slow horses”—a play on the name of their workplace. Yet, while the operatives are supposedly relegated to dead-end jobs, with the expectation they’ll eventually quit out of boredom, Lamb’s group becomes involved in missions that threaten the safety of Britain itself, shaping the team’s redemption arc.

Over its four seasons thus far, the “Slow Horses” cast has featured a vast array of talent, including:

• Gary Oldman as Jackson Lamb
• Jack Lowden as River Cartwright
• Kristin Scott Thomas as Diana Taverner
• Rosalind Eleazar as Louisa Guy
• Aimee-Ffion Edwards as Shirley Dander
• Saskia Reeves as Catherine Standish
• Christopher Chung as Roddy Ho
• Kadiff Kirwan as Marcus Longridge
• Chris Reilly as Nick Duffy
• Jonathan Pryce as David Cartwright
• Ruth Bradley as Emma Flyte
• Freddie Fox as James “Spider” Webb
• Dustin Demri-Burns as Min Harper
• Naomi Wirthner as Molly Doran
• Bally Gill as Agent Singh
• Hugo Weaving as Frank Harkness

Nina Gold (“Game of Thrones”) and Melissa Gethin Clarke (“Apple Cider Vinegar”) have been casting the Apple TV+ series since it premiered in 2022.

Gold told us that one shouldn’t take rejection personally. Just because you did not get a certain part does not mean your performance wasn’t stellar; it simply means you were not who the CDs were looking for in that particular instance.

“If they don’t get the part, it’s not because they did something terrible or wrong or they were bad,” Gold shared. “It’s normally not that, it’s just such a delicate, hard-to-define thing that makes one person more right than the other nine people trying the thing. That thing is really hard to determine. There are certain factors about the way that the part and the actor are right for each other that has nothing to do with your audition. It doesn’t mean that the fact that you didn’t get the part is because you’re not talented or great. It’s because there was something else that was more of a perfect fit with someone else. Each situation really is unique.”

Gold told Casting Networks no actors were attached to this series when she joined the project. Instead, the team’s first mission was to secure Oldman. “We tried to get Gary Oldman and started there. When he said yes, we were absolutely thrilled,” she said. “Then we took it from there.”

But his confirmation shouldn’t have come as a surprise—at least not to Oldman’s longtime collaborator, executive producer Douglas Urbanski. He told Deadline the lead was already in the market for this exact role. “Gary Oldman was sitting on my sofa,” Urbanski shared. “I think he said, ‘Can I have a role where I don’t have any prosthetics, or I don’t have any wigs, where I don’t have any costume changes, where I can use my own accent?’ And I said, ‘Those are very hard.’ And he said, ‘Maybe something with spies.’ I said, ‘Those are very hard to come by.’ About a week later, ‘Slow Horses’ landed on my desk. I read it on the plane. We were going with a Soderbergh film to Venice and [Oldman] said to me, ‘What are you reading?’ And I said, ‘I’m reading your new best friend. His name is Jackson Lamb.’”

Once Oldman signed on, Gold and her team had to then go about casting the ensemble surrounding the award-winning actor. “We [cast] it through a lot of meetings and auditions. Everybody wants to work with Gary. And Gary is very generous to other actors and very cool to work with,” Gold explained. “In Season 1, we began in person, and after the pandemic started, we did a lot more over Zoom. Eventually, we would meet people in person at, like, a million miles away from each other wearing masks,” she noted.

“It’s much better to meet people in real life, but you have to make it work, regardless [of] which way it is,” she said, while also touting Zoom’s benefits. “Over Zoom allows many more actors to have a go at it and allows you to audition more people. They don’t have to be available to meet in northwest London on a Wednesday afternoon!”

Deep down, Gold always has everyone’s best interests at heart, especially during the stressful audition process. “I feel for all the actors who have to walk into the room and make it work at the click of a finger. It’s difficult,” she said. “I hope they remember that, as casting directors, we’re on their side and want them to get the part. We are here to help. I appreciate how extremely difficult it is. I mean, I couldn’t do it, my God! […] With auditioning, you are put on the spot. Once you’re playing the role, you have much more information and input to make a complicated version of the character. When you’re auditioning—especially nowadays—nobody gets to read anything properly, so as an actor, you are hoping you’re giving it the right approach.”

“Sometimes when it may not have been quite right, but they seemed good, you let them have another go and try again. Or maybe you think, ‘Wow, they’re really good,’ but now you realize that part should be a 17-year-old female instead of an 18-year-old boy. Factors like that could rule people out just as quickly sometimes,” Gold concluded. “Ultimately, somebody must somehow whittle it down to only one person playing that part, with that one person being the right person.”

Apple TV+ renewed “Slow Horses” for Seasons 5 and 6 in 2024, with the former having wrapped filming in late 2024. Season 6 started production in January 2025. Unlike previous seasons, the sixth installment will cover two books, the sixth and seventh, in Herron’s series, which currently features eight books, with a ninth novel due in September. Might the Apple TV+ series ultimately come to an end after Season 7 or 8? Stay tuned to this page for updates!

There are no open casting calls available for “Slow Horses” at this time. While we recommend getting an acting agent if you haven’t yet, you may also want to peruse our guide on auditioning for Apple TV+. We suggest bookmarking our directory page for UK casting calls, as that’s where the series films.

Don’t count yourself out. As Oldman once told us, actors have a tendency to convince themselves they are no good before they even step inside an audition room—but they’re usually completely wrong. “I was given a piece of advice once, which I thought was good,” he said. “I was very nervous and worried about an audition—this is many, many years ago now, I’m talking early 1980. I wanted very much to work at a theater company called the Citizens Theatre; it was very renowned, and it was one of my ambitions to work there, so I was more nervous about this particular audition. And a young director that I had done a little bit of work with said to me, ‘When you go in to do this audition, you’re probably going to be one of the best actors they’ve seen all week, because you have this thing in your head that you’re less than.’” 

“I still have it. I think it’s the natural thing of the performer, or someone who is creative: egomaniac with low self-esteem. You’ve got to have something that pushes you forward to just get up there in front of people, and yet there’s a vulnerability and insecurity that comes with it. I think that’s what keeps driving you to get better and better and better,” he continued. “But I remember it really helped; it did take the edge off the nerves. And take your time. Breathe and take your time. If they’re horrid to you, then maybe they weren’t worth working for anyway—that’s what matters. That’s why I always think it doesn’t cost very much to be polite and to be nice.”

Avoid the naysayers.  Pryce told us that, as a young artist, he didn’t receive much encouragement in pursuing his craft. In fact one of Pryce’s tutors told him he’d never play anything more than villains on TV—so he went out and got a new tutor. It was in that moment Pryce learned you must eliminate negativity if you’re going to succeed. “I think that’s the only advice I can give: Get rid of the naysayers around you,” he said. “Don’t just listen to people who say you’re good, but learn from that negative energy and turn it into positive energy.”

Of course, he also noted that had he taken any other sort of advice during those early days of his career, he likely wouldn’t have achieved the success he’s attained in the years since. “I think any good advice, any sound advice would mean I wouldn’t be sitting here talking to you now,” he shared. “I would have said, ‘Work harder at school. Do your exams.’ If I’d done that, I wouldn’t be here. So…stay naughty!

Don’t let rejection slow you down. When Kirwan first began performing in school, he hid the fact from his sports teammates because he was afraid of what they’d think. But as it turned out, they were nothing but proud of their friend. “[A]t the end of my number they got up and cheered. After the show they were like: ‘Mate—we’re so proud of you, why would you hide this from us?’ I missed out on a lot of time that I could have spent sharing that joy with my friends for fear of rejection and ridicule,” Kirwan told us. “So, be fearless and be honest.”

After all, rejection is part of the job description, so don’t let that scare you away from embracing what brings you joy. “Rejection never really gets easier. It’s less painful when you actually get the ‘no’ but often you don’t hear back at all, which is awful. If someone’s going to present their work to you, the least you can do is let them know,” Kirwan added. “But you have to know it’s momentary. You might be out of work for months but something will come along. It’s just the nature of the job. Now, if I’m free in any way, I write. It’s a passion I can do between acting. But if that falls through, I pull a mean pint.”

Gold echoed the sentiment, saying, “Only become an actor if you absolutely have to because it’s pretty difficult to do. You have to get ready to put up with a lot. There must be incredible highs, but also lots of disappointments and rejections, and learning to accept that is part of the whole of the job.”