It seems a reoccurring worry, an almost niggling thought that appears each time Jack prepares for a role, something he dubs as hilarious. But this time, it’s different, as returning to his role as River Cartwright in Slow Horses, he feels reassured and fearless. “For the first time, I’m playing a part I’ve played before. This role in Slow Horses has been the turning point for me in trying to get rid of that fear and feeling a lot more secure.” Growing up on stage, Jack tells me how his fear of failure partially stems from performances set in film. “On stage growing up, you would do it again and again. So, if you fucked it up on Monday, you could do it again on a Tuesday. And I’ve struggled with that, the idea of whatever you do, it’s burnt in. You can’t do it again on the DVD. It’s gone, and then it’s there forever. So, every time I go into a role, there is a battle of how I will do this every time.” How have you coped with that enormous pressure you feel, I ask? “For most of my career, I’ve coped with it badly - to the point where I’ve wanted to stop - and in fact, I did stop at one point. It was through just feeling like I didn’t know what I was doing and not knowing how to do it. I guess it was a level of self-criticism that was just unhealthy and, really, a waste of time because it’s film and TV. That’s what we’re making, you know, we’re not doing anything else.” But we know it’s more complex than that.

As I reassure him of its importance, Jack speaks candidly about those who had supported him over the years when he was suffering from anxiety. He tells me of moments in his 20s when he relied on occasion on family and friends when battling panic attacks. “There was a film I did about seven or eight years ago. One scene in particular, although it was a simple scene, I just started to panic. I was thinking I don’t know what I’m doing. I don’t know how to do this. I rang a friend in between takes and stood there in a period costume and a fake moustache. I remember saying I don’t know what to fucking do, and can you help me. He talked me down off this ledge (metaphorically) of me wanting to stop halfway through the film.” In an environment that can be all so consuming, where you are your product, Jack tells me of the pressures of being unable to leave your job in the workspace. “Whether that’s a piece of art, whether it’s a kid that you’ve taught, or someone that you’ve nursed back to health, you’re still separate from your work. The majority of people go somewhere, they do their work, and they can leave it, and they can walk away. There are probably many people who would argue that they have the same problems in their job, and probably some of the jobs I just mentioned make it tough to pull yourself away from. Still, we are the job, and it can be quite difficult if you’re not fully comfortable within yourself.” At the same time, dealing with the struggle that comes with confidence, I wonder when it changed for Jack. “Sadly, it wasn’t able to change for me until I felt like I’d worked out how to do it; how to act in a way that I thought was good.”

Fake it until you make it, whereas his returning role seems to lean on a process he’s already worked through. “It’s the first time I’ve ever done that. And it changed me being in a recurring role. We’re doing season three now, and it’s just such a joy not to be thinking the same things I was thinking before the first series; who the fuck is this I’m playing, and how the hell am I doing that? Having series two under our belt means there’s much more space in your head and much more creativity. I have access to more of my ability and creativity.”

As Jack lets me in on the extra headspace he’s been able to take full advantage of while visiting a role and character he knows well, with reading being an evident passion of his outside of the job, I can’t help but question whether that space is filled with part of the characters or roles that you hear often get taken home mentally. “I’ve never struggled with taking on a character’s burdens. Things that the characters that I play go through or experience, I leave with them. As soon as we go home for the day, or the curtain comes down on stage day, I leave it behind. The thing I love about acting, which sounds like a stupid thing to say, is I get to be one thing one minute and another thing the other. I have no interest in being the character off-stage or off-camera. It’s not how I work. And it’s not how I work well, either. It took me ages to realise what works for me is just to be me and revel in the fact that I love that magic moment where you step from the wings of that stage, and one minute you’re Jack, the next minute, you’re someone else.”

As for taking on the role of producing a film, let alone the delicacy involved when adapting a memoir to film, Jack explains the risks he took without crossing lines. “It is a delicate topic, I think, when it’s a memoir of someone who is unbelievably honest, and the centre of it is addiction, alcoholism, that the character struggled with and still does. It’s delicate. That’s why we had Amy involved as much as she wanted to be. She co-wrote the script with the director and was there on set as much as she could be, but we also talked about boundaries, and she understood that she would have to have a certain distance. You have to go at it with the right attitude, not too tentative. You’re not pussyfooting around, because that’s another mistake you can make if you’re too cautious and presumptuous, but it was wonderful.”

“We had to shoot in some challenging places where people haven’t shot feature films before, but the people of Orkney were fantastic. They welcomed us; me and my producing partner, Dominic Norris. When we walked onto the island, went into the village hall, and pitched the idea that we would do a film there, we were open to questions and any concerns. And we did that two or three times. It was challenging, but the people were wicked. They’re proud of it.”