At the age of 27, Rose Leslie has already won a Scottish BAFTA and starred in two of the biggest global TV dramas of recent years, Downton Abbey and Game of Thrones. Now, she’s starring in the new series of Utopia, Channel 4’s unique, ambitious and acclaimed drama, as the youthful Milner. Here, she discusses the fun of playing pure evil, and why Milner is a character that fascinates her.

The first episode of the new series of Utopia is a bit different, isn’t it? Explain what it’s about.

It is. As a really big fan of the first season, I thought it was a brilliant idea. It basically takes us back to the 1970s and shows us where it all began. We get to see Milner as a young woman, and we get to see why she turns into this ruthless killer. And we see what happens to Carvel as well, and how Jessica and Arby come to be. I was completely hooked by the concept. It’s really a stand-alone episode, and a real treat for the fans.

Milner’s a real hard case, isn’t she? Is it fun to play someone so bad?

Oh it is so much more entertaining playing an evil person than playing a sweet, charming young lady. Before I even went in for the audition, reading some of the scenes and the stuff she does, it was breathtaking. I loved it. As an actor, it was an absolutely thrilling role to play. It was so exhilarating to be such a horrible character.

The 70s are really evocatively recreated. Did you do anything to try and get yourself into a 70s frame-of-mind?

I felt the clothes did a lot of that. The costumes were brilliant – there was a lot of tweed and a lot of beige. That definitely helped me, as did the hairstyling, with the soft curls, particularly at the bottom of the head, that really transported me. And I grilled my parents on what the 70s were like. And I also felt like there was a lot of information that I could use in the script.

The script weaves in some key news stories from the 1970s. It’s very cleverly done, isn’t it?

It is so clever. That was one of the reasons why I was so thrilled to get this part. I think Dennis Kelly is a genius – both his stuff for screen and his plays – and the writing was superb. That’s what hooks the audience. All the garbage on the streets and so in is incredibly evocative of the time, and some of the political intrigue, the way the Airey Neave story is woven in, it’s brilliant. It was a real history lesson for me as well. I was embarrassed about how little I knew of the 70s.

It sounds like you were already a fan of Utopia. Did you watch it when it went out?

I did. I was all over it. It was word-of-mouth for me. I remember talking to a girlfriend of mine, and she told me about this new drama that had started the previous night, and she said that it was unlike anything she’d ever seen on TV before. So obviously that piqued my interest, and I went home and watched it. And the colouring, the direction, the editing, the acting, it was just incredible. So I was a little bit late on the first episode, and then, of course, I watched it every week that it then came out.

When you were cast as Milner, did you then go back and study how Geraldine James had played the role?

I went back and studied it, and of course that was a great excuse to watch the whole series again. So I was very happy to do some homework. But I was also aware that it might become something of a hindrance to then try and pick up her voice and to recreate each mannerism. Of course, as human beings, we develop through time. We develop, we change, and we’re not the same person we were 20 years ago. So I felt that allowed me some artistic license to interpret the character as I saw her as a young woman. But of course it was great to watch Geraldine do her work, and she does Milner magnificently. She sets such a high standard, the thing that really worried me as would I be able to be convincing enough that she would seem to be the same person.

The fascinating thing about Milner and the Network is that there’s a twisted morality at the heart of what they’re trying to do, isn’t there?

Yes, there really, really is. And what’s terrifying is, playing her for a full month, you can see the reasoning, you can see where she’s coming from. They’re doing it for the greater good. They’re doing it for the longevity of our species, giving it the chance to thrive. You can totally get swept up in that. But then you see the lines start to blur, you see what she has to do to make things happen. They can’t afford to have friends, they can’t trust anyone, they have to commit the most terrible acts. That makes you step back and think. But that’s the beauty of Dennis Kelly – he writes it in such a beautiful way, you’re able to see both sides of the argument.

You’ve had a pretty amazing few years, starring in Downton Abbey and Game of Thrones. Those experiences must have changed your life.

They really have. I’ve felt hugely privileged, from the bottom of my heart, to have been a part of those two shows. They were wonderful platforms – being part of something that’s popular is a wonderful springboard for any actor. I had an absolute blast on Game of Thrones – they were the best three years – meeting all these amazing people, and working with fantastic crews, and going to these incredible locations. I would never otherwise have gone to Iceland, and now I have a great love for the country.

Is it true you had no idea how big Game of Thrones was until after you’d auditioned for it?

Yes, and it’s the first time in my entire life that I’ve been so happy to be ignorant. If I’d had any idea just how popular it was after the first season, I think I’d have been far more nervous walking into that room. Luckily, it just felt like another audition to me. By the second round, I’d clued up and done my research, and I managed to get the part. But the first stage is always the toughest, and I walked into that room blissfully unaware. It could all have gone very differently.

Do you get recognised a lot now? How do you find that experience?

I get recognised quite a bit from Game of Thrones, and so far it’s been great, because the fans are so passionate about it. People just want to come up and have a picture taken with you or have a chat, because they love the show. It’s been a great experience. Now that I’ve said that, I’ve jinxed it. I’m going to get eggs chucked at me and be abused in the street.

Your first big project was New Town, a Scottish drama set in Edinburgh. You won a Scottish BAFTA for that. You must have thought this acting game was pretty easy at that stage.

Noooo! I think the wonderful thing about having gone to drama school is they made every single person well aware of just how cut-throat and hard this industry can be. So I was all too aware that it’s a marathon, not a sprint.

Are you a proud Scot?

I am a proud Scot. I consider myself Scottish, but I also consider myself British, and I want Scotland to stay within the UK. I’m very passionate about that.

Which actors do you particularly look up to? Who would you really like to work with?

There are so many that I’d like to work with. I think Andrea Riseborough is astonishing, such an amazing talent. I’d love to work with her, and with Cate Blanchett. I’m a huge fan of Mark Rylance too.

What do you watch for your own entertainment?

I have just finished Breaking Bad. I can’t believe I was such a latecomer to it. It was phenomenal, every single episode. I’m ashamed to say I watched the whole thing, every series, in about five weeks.

Utopia will broadcast from 14th July, Channel 4, 10pm.