You play Dee in National Treasure. Explain a bit about her.

She’s recently come out of rehab, she’s living in a halfway house and she has two children that she’s estranged from because of that. Her ex is about to try and get custody of the kids and that is kind of sparked on by what happens with her father, Robbie [Coltrane]’s character. That’s the catalyst. She’s in a lot of isolation at the minute, she’s on her own in this halfway house.

How much do her problems come from her father’s career and his fame?

I think a lot of people have addictive personalities, there are many addicts in the world and not everybody’s parents are famous. I don’t think that’s really the thing to focus upon. In terms of her dad, he could work in a bank and she’d be going through the same thing. They also have a really strong relationship as well. She was always closer to her dad than her mum. The relationship between Dee and her mum is understandably competitive, because they’re both dealing with a person who has very little real time to give them.

What attracted you to the project?

Marc [Director Marc Munden]. When Marc asked me to do it, nobody else was in it. It was Marc and me in the beginning. I would work with him every day of my life. I love him. He really cares and he’s uncompromising. He is very compassionate. He’s a bit odd and I like him for that reason. I feel like we’re in good company with each other. He has an unusual way of looking at the world and I really enjoy that. I read the script and as soon as I read the script, I knew exactly why he thought that I’d like it. It’s really beautifully written, it’s a beautiful piece of writing. Dee, especially, is a great character because she’s kind of sexless. A man’s written her, but it’s not like you’re reading a woman through a male filter – he’s [Jack Thorne, writer] written her as a person. I really enjoyed her androgyny and her humour. Her humour is very, very different to mine, but I really enjoyed it – her sarcasm! I’m a bit more of a softie, I’m not really very like Dee at all, but I do identify with things that she’s been through in her life.

The subject matter is pretty sensitive and potentially controversial. Did you have any misgivings about taking it on?

No, that’s my job. I think it’s part of the way we process things. Things are difficult for us to process, so something like this helps us to do that. We get to hold a mirror up to ourselves and society.

Did you do anything in particular by way of research? For example into recovery from addiction?

I didn’t need to – I had a lot of knowledge. With Marc, he and I tend to work in quite a physical way. I really felt like we created Dee together. Obviously apart from the fact that she is so wonderful on the page. She could have been interpreted as anything. She might have been wearing a power suit. She could have been any character in the world. But I had this idea of who she might be and Marc is great at pulling that out of me. He’s a really caring and nurturing director and there’s no rush to find anything. We did a lot of rehearsals. I can tell that he enjoys watching the characters develop.

How did you find working with Robbie and Julie?

Julie is a hero of mine, she’s phenomenal. We just laughed and laughed. I guess we’re from quite similar places. I really identified with Julie growing up, being from similar backgrounds. I haven’t seen it, but I know that it’ll be really, really good – I think that Marc is really good at hooking the cream off the top. I’m really excited to see what he’s done. Parts of it I’d seen when we were filming, but I try not to watch the stuff that I do. I try to stay inside of it and not get too objective about stuff. But the parts that I did see, it was shot so beautifully, and the spaces between the characters were so painfully wide, even when they were very close together. Marc has a great eye and a great ear.

You’ve worked with some of the biggest names in showbiz. Do you ever get intimidated or star struck?

It seems like everybody’s so obsessed with that – whether people are known or not and what it’s like to know people who are known. I guess that’s very human. I think it’s very important when you meet people to just meet them face-to-face and understand they’re a human being. That’s always been my experience. I suppose the answer to the question is, “I’ve never thought about it”. Maybe that makes me a weirdo, I don’t know. I know that’s not the answer people want to hear. They want to be told “It’s so amazing, I can’t believe it,” but that’s just not been my experience. I feel very, very fortunate to have worked with some brilliant artists and Julie is one of those artists, definitely.

What work are you most proud of?

Well, I don’t actually go back and watch my work, but I think the work I’m most proud of is Silent Storm, which is a film that I made with Barbara Broccoli. It was made at a time of my life when I was going through a lot of change, and I think that is some of my proudest work. The whole film is me being abused on an island in the middle of the Hebrides, no-one was ever going to watch it! But it was absolutely my cup of tea and I felt very excited about the work that I did on that.

Does it follow that the work you enjoy making the most turns out to be the best?

I don’t know. How do you quantify what’s the best?

What you’re the happiest with, artistically?

I don’t approach it like that, I guess. Like I said, I don’t really watch things that I’ve been in. I think that affords me the ability to not be self-conscious. I just wouldn’t be able to tell you what was the best? I also think because the work you do as an actor is so subjective, I may have thought the film that I was in was terrible, but 200,000 people in America thought it was great, or whatever.

What do you look for in roles these days?

Just the right fit, the right thing. That’s the simple answer. When it’s just the right thing. When you read it and you just think “This is really interesting to explore.” There’s certainly a lot of things I would never look at. That I’d never even open. But then there are things that people who I work with know to never send me. They know it’s not my taste, in the same way that I wouldn’t send them a birthday present that I knew they wouldn’t like. I work with a group of people with incredibly good taste. I don’t know how that happened but I thank my lucky starts for it.