For her role in the film adaptation of the bestseller The Girl on the Train, Emily Blunt was excited to get her head around a character unlike anyone she's ever played. "Rachel is very toxic, physically and emotionally," she says of her character. "She's an incredibly tortured, self-loathing sort of person, and I thought it was thrilling to have a protagonist that's a blackout drunk! So it was a combination of the personal challenge for me."

Emily Blunt's character sipping on a Martini in The Girl On The TrainEmily Blunt's character sipping on a Martini in The Girl On The Train

After playing a series of more heroic characters in films like Into the Woods, Edge of Tomorrow and Sicario, it was fun to play someone who was so unreliable. "Even if I don't agree with the things that she does, I have to understand her and empathise with the fact that she's taken life's setbacks harder than most people," Blunt explains.

Playing an alcoholic wasn't as easy as she thought it would be "it was really hard!" she laughs. "I think it is tough because it can look comical, and I did not want people laughing in the movie theatre. But when when you're up close with a real drunk - and I have been up close with a real drunk - I think it's quite a scary thing. That's more what I looked for: how can I be most unsettling to be around?"

And the role came with extra layers of self-doubt, including the worry that she might have killes someone. "I've never played somebody as tortured as this," Blunt says. "Not just the addiction, but also somebody who's afraid of themselves. And you've got the heightened environment with a potential murder. That combination is like a real character piece with the combination of a thriller, so it's really unusual. It is a rarity in Hollywood to have a mainstream film with such a flawed character, especially the female character."

Blunt says that multi-faceted female roles like these are important for cinema. "I wish we would talk less about it and do more about it," she says. "Talking just cements the issue further rather than actually moving the needle. We need to be creating roles where you've got diversity, creating roles where you've got very multi-layered female characters, and I think we need to hire more female writers and more female producers. We need more conscious people behind the lens, and therefore we're going to have more people in front of the lens who are going to support this movement."

Watch the trailer for The Girl On The Train: