Warning: This interview contains spoilers for ‘Black Mirror: Bandersnatch’.

‘Bandersnatch’ is the game-changing ‘Black Mirror’ event that had everyone talking upon its release at the end of the last year, and the man at the centre of it all was British actor Fionn Whitehead.

While still in the early stages of his acting career, Fionn has already starred in a wide array of differing projects, including the Oscar-nominated war epic ‘Dunkirk’ and the BBC’s monologues series ‘Queers’.

‘Bandersnatch’ sees him on completely new ground, as the story follows his character – Stefan, a video game developer in the early 1980s – on his journey, which is almost entirely dictated by the viewer, as they make choices on his behalf.

HuffPost UK caught up with Fionn to talk about the difficult filming process and the storyline he was “annoyed” to see didn’t make the final cut. Here’s what we learned over the course of our interview…

Already a ‘Black Mirror’ fan, he was ready to sign his name on the dotted line before he even knew the details of the episode

“Even before I found out the script I was like, ‘I’m probably just going to say yes to this, because I love Black Mirror’. But then once I found out what it was, it kind of made me even more excited. And then when I got the part, I was over the moon.”

He was kept in the dark about the nature of the episode until almost the last minute

“I had a meeting with Charlie [Brooker] and Annabel [Jones, the show’s executive producers] after I’d been offered the part, and I’d only found out it was going to be an interactive episode a couple of days before, in a really quick email. And that just kind of said ‘it’s interactive’ and ‘it’s about video game coders from the 80s’.”

The multiple timelines and story twists didn’t make things easy when it came to learning his lines

“Sometimes you have to say the same lines in a slightly different way. So when there’s a variation of a scene, because the audience has gone back and there’s a montage or whatever it is, for whatever reason, sometimes the words might be the same or very similar, but you have to say them in a way that is slightly more aware.

“And that’s something we’re not used to in acting, because a lot of the time you’ll have your set way that you read something, and although you might vary from it in every take to try different things out, for the most part you have your idea. For that reason your intonation and tone will generally stay the same.

“Whereas, with this you were forced to break that up a bit. Also, it meant you had to be like… certain words, you really had to hit… for the clarity of the audience, you had to be very on point.”

But it was actually time constraints during the filming process that proved to be one of the toughest aspects

“I suppose one of the most difficult things was the amount of dialogue we had to get through every day, because of the time constraints. So that was definitely difficult… just the amount of time we had to shoot the amount of material we had to get through.

“It was filmed between six and seven weeks, and there were four and a half hours of coverage that made it into the end product. We shot a lot more, that didn’t end up getting used.”

One cut scene would have offered viewers an entirely different possible ending and Fionn says he’s “annoyed” it didn’t wind up in the final cut

“There were some things that I’m actually… not disappointed, but annoyed it didn’t make it in. Because I found the concept very interesting.

“There was a particular choice point that didn’t make it in, and that was upon meeting Colin [Will Poulter’s character] at the door of the house, there was a choice point where Stefan pulls a knife out, and the choice was to stab Colin or drop the knife. And if you dropped the knife, Stefan had a breakdown and collapsed into Colin’s arms, and kind of gives him a big hug, which is clearly what he needs, really.

“So I’m a little bit…. that was quite a nice touch, that didn’t make it in.”

Despite some of the more gruesome moments in ‘Bandersnatch’, it was Stefan’s anxious tics that Fionn found especially difficult 

“Playing such a highly-strung character is quite a difficult thing to do because it requires a lot of energy. It’s a very high-energy piece, because even in moments of stillness with Stefan, he’s constantly anxious and being tense and it spirals and gets and worse. It’s a high-energy thing to maintain, and so that was very tiring.

“Not taking it home with you is a skill that I would say that a lot of actors are constantly getting used to and working around and with, because it is definitely, whether you’re a ‘method’ actor or you’re not, playing a role where you are trying to inhabit a character with such a different psyche to your own, it’s a given that it will have some kind of effect on you.

“Maybe the only effect it’ll have is that your shoulders are tight when you go home, maybe it’ll be worse than that. But it’s important to have your own kind of ways to shake that off at the end of the day, whether that’s playing relaxing songs, getting home and doing a bit of meditation, or whatever it is, or just having a bit of time to yourself where you can leave that character behind.”

There was a fair amount of stress on set too

“I think it was true for everyone, that it was an incredibly hard shoot. It was great, an incredible thing to do, and everyone was very passionate about it and of one mind in terms of everyone thinking it was such an interesting concept.

“But it didn’t change the fact it was a very hard thing to shoot, because we were essentially the guinea pigs, of this format of television and film.”

And even though he felt for Stefan, Fionn doesn’t agree that viewers should have been given the option for him to have a happy ending

“I think it very much follows the ‘Black Mirror’ format of general bleakness. And I think that it definitely works for the piece as a whole that all the endings you get are fucking dire. So personally, I think that works. It doesn’t upset me particularly that there is no happy-clappy ending. That is ‘Black Mirror’, really.”

‘Black Mirror: Bandersnatch’ is now streaming on Netflix.