Your performance in Submarine is undoubtedly one of the biggest British breakthroughs of the year. How did you get involved?
I’d done a lot of kids’ TV before it and I hadn’t worked for about six months, to be honest. When the script came through, I was just like, ‘It’s work!’ But, obviously, it turned out to be amazing. From reading it you could tell how funny it was, and that was just an early draft. So I [auditioned] for it, and then got a callback a couple of weeks later to meet Richard. That was really cool, because I got to improvise with him. I think anyone who improvises with Richard is going to look funny, even if they are not. Then I got another callback, and that led to the screen test which was with Yasmin [Paige, who plays Oliver’s love interest Jordana]. And it was a really weird screen test. Usually it’s just you in front of a wide screen, doing a few scenes, but this one was a two-day shoot in Wales! We were thinking, ‘Do we have the part?’ but we didn’t want to say anything because we thought that at any moment Michael Cera and Ellen Page were going to step in and take our parts! With Ben Stiller being attached as the executive producer, I really did think there was not much of a chance for this kid from South Wales.

In Oliver you created a character who is very unassuming, but also very memorable. How did you get into the role?
I’d never done any dry, deadpan acting before. If you look at my kids’ TV stuff, it’s mostly me prancing around! Richard sent me a few films like The Graduate and Rushmore and Harold and Maude, and I looked at those films and I could see what he was going for. We had a week of rehearsals, and got the character down there. I was really happy, because I love Michael Cera and Jesse Eisenberg and all those really dry actors, so this film was a dream come true.

Most people know Richard from The IT Crowd. What was it like working with him?
I hadn’t seen him in The IT Crowd before I did Submarine, and I think that was the best thing. If I had, I would have been like, ‘Ah, it’s Moss!’ Instead I got to know him as a friend. He’s such a quiet and shy guy but there’s so much going on in his head. He’s constantly thinking, and I think he really is a genius. He’d give us some freedom. He’d be like, ‘Well, if we get some time here then you can do some improvisation, and see how that goes.’ So that was really cool, but I really didn’t think there was a need for that because the script was so bloody spot on.

Submarine has been a huge hit; why do you think it’s found such a large audience?
I think it’s the connection it makes with people. People can relate to it, it really hits home with a lot of people. And I also think it’s because people love Richard, because it has Alex Turner doing the soundtrack, and Ben Stiller is attached to it… I think it’s just a really good recipe for a good team.

And it’s got an amazing cast, too. Did you learn a lot from co-stars like Noah Taylor, Paddy Considine and Sally Hawkins?
Definitely. I just learnt how chilled out they were. Seeing that, I was like, ‘That’s the best thing to do. Just relax. Don’t stress out about it, don’t get too nervous.’ I hadn’t seen Sally in Happy Go Lucky before Submarine, and I’m really happy that I didn’t because I would have been nervous and intimidated. I’m a huge Paddy Considine fan, the guy is a genius; there’s no better improviser. And Noah Taylor, hands down, is the funniest guy in the world. I was just like, ‘Wow. Don’t say anything. I don’t want to fuck up!’

When Ben Stiller came to the set, did he offer any advice?
No, he was just like, ‘Hey, how’s it going?’ I was just like, ‘Good, good, how are you?’ And he was like, ‘Yeah, I’m good.’ I didn’t know what to say to him. I remember stuttering and saying ‘Greenberg was brilliant, well done’, and then feeling like an idiot after saying that! And then I went home that night and thought, ‘I had a conversation with Ben Stiller, that’s insane’. I got completely starstruck. At the end of the day, I really am just a kid from a small town in South Wales. It’s still all new to me.

But you haven’t had any formal training?
No, I’ve not been to any drama schools or anything. [I was] about 10 when I got my first job. I’d gone to a stage coach but only for a couple of months. I quit straightaway because it was so boring, singing and dancing. And also because I wanted to play football on a Saturday, and stage coach was on a Saturday! I’ve not really had any training, and in a way I’m glad. It can change someone for the better, but also for the worse. I really don’t think it’s necessary. I suppose if you’re meant to do something then you’re meant to do it. It’s a personal choice, isn’t it, of whether you actually want to do it or not.

Submarine has kick-started what looks to be an incredible career, and you’re working on some interesting projects. What do you hope for the future?
I just want to make really good films, and I’m really interested in writing. I’ve got my own sketch show that I’m trying to get off the ground at the moment. It’s called Bruce Andrews, and it’s basically about a kid from Wales that gets a lucky break, and goes big-headed and stuff. It’s spoofing myself. I’m also starring in it. I’ve not got it off the ground yet, but I’m talking with Funny or Die in America about maybe doing something. I would like to work over there a lot more.

Do you think going to America is a rite of passage for young British actors?
No, it’s just because I love the show Entourage! I want my own entourage in LA!
Submarine is available now on DVD & Blu-ray from Optimum Home Entertainment