From the moment she hit the big screen in Atonement, Saoirse Ronan had proved she was a genuine star. The Irish starlet is one of the very few child actors who have managed to make that leap to certified A-lister effortlessly, Ronan has excelled where others have failed over the years, sidestepping the Hollywood social drama and concentrating on her talent and career, and boy has it paid off.

We sat down with Saoirse just a couple of weeks ago to have a chat about her new film, How I Live Now, and to discuss some of her upcoming work. As always, she is in good spirits, chatty and always engaging.

We began by talking about the book behind the film, and how she felt about the screenplay: "I've always found, unless it's about a real life person, and the script is strong, and has a good structure, it's better to just focus on the screenplay. With the book, there are a lot of characters that were taken out. It was basically the same story, but things had been changed and shifted about a little bit.

Her character is very different from anything Saoirse has played in the past: "She's a bit of a bitch. (Laughs) I was a bit worried about being pigeon-holed in that category. It was obviously quite a respectable thing but at the same time, I didn't want to get into a habit of playing those kind of roles and people seeing me in those kind of roles. After the Host finished, I had played a vampire, Hanna, an alien and I really wanted to play a normal girl, who was very current. Daisy is a very modern girl, with a lot of modern insecurities, paranoia's; that drew me to her."

How I Live Now is certainly dark in a lot of ways, something Saoirse readily admits: "I was glad it wasn't Hollywoodised, I felt like this could easily happen. You don't know who the attackers are or where they have come from or what they're reasoning is. This film is about lost love and trying to get back to the person that you love. It was very emotional but if I can't leave that behind at the end of the day..."

Kevin Macdonald, director of How I Live Now and the Last King of Scotland among others, was one of the main reasons that Saoirse was so interested in the role: "He's not over sentimental, he's not too sappy about anything. He has a lot of respect for the emotion of a scene and what the actors can bring to it. He had a challenge on his hands, he worked with a cast of pretty much newcomers."

Of course, we had to ask her about that upcoming film with Ryan Gosling, How to Catch a Monster, something Saoirse can finally talk a little bit about: "We finished it in June and it was brilliant. I had just finished a Wes Anderson film which was in every way the opposite of How to Catch a Monster. I went on to Ryan's film and everything was improvised. You did what you felt on the day and that included where the story went and how the relationships developed. He got so much footage out of us trying to figure out stuff. Every day was a surprise."

Ronan spoke a little about her lifestyle, particularly some of the influences of the social scene in LA and how easy it would be to get sucked into it: "It would be very easy to get sucked into it, I know that. but because I started when I was younger and always had my parents with me, I developed a mindset which was a different way of thinking to most people in Hollywood. I'm just not like that. I can handle LA and can appreciate the good parts and have a lot of friends there. You just have to make sure you are not listening to people who are telling you that you're amazing all the time."

"After Atonement, I still had the innocence of being a kid, and I think kids have that instinct throughout their childhood. Kids either think, I don't like you or I do like you, it's black and white for them. It's a learning process and that happens in life anyway!"

Confirming that she is playing Mary Queen of Scots next year, Saoirse is particularly excited about the role: "I feel like I need to fully understand who the Tudors were, who the Stewarts were and the family politics. It's so cutthroat, everyone screwed her over. That's what is so heartbreaking. I'm really excited about that."

There had been a couple of questions about her beauty regime and how she prepares for events: "I have a stylist in the States, Sam McMillan and my best friend is my stylist here, Grace Moore. I have relationships with certain designers, I wear a lot of Miu Miu. I prefer to have relationships with people where I know I will wear their stuff. I love Mary Katrantzou. The rest of the time I like to wear Topshop and Urban Outfitters!"

Saoirse plans on continuing on with the film plans for the future: "There's a few actresses who are so wonderful, if you can emulate that, I guess that's great. I mean, there's no one really better than Cate (Blanchett). She's always done stuff that she cares about and played strong characters, real women."

Is that how Saoirse wants to approach her career? "Yes, I mean that's what I believe in. There's no way I could do something for three months to a year of my life and not care about it. But that's with anything you do!"

How I Live Now will be in cinemas on October 4th.