Emily Blunt is curled up on a sofa in a West End hotel suite, wearing a cream dress peppered with black dots. It is a few weeks before her 27th birthday; she has long brown hair and blue Cleopatra eyes laced with a knowing wit. (Those eyes once prompted an ex to nickname her "Garfield".) On screen Blunt has sometimes cultivated a certain haughtiness, which she has described in the past as her "head girl demeanour", but in person she's fizzy and easily amused, without a hint of the withering cruelty displayed in The Devil Wears Prada or My Summer of Love.
Hers may be the sole face on the poster for The Wolfman, the remake of the whiskery 1941 horror favourite, but she would surely be the first to admit that audiences won't be flocking to see how she handles riding a white steed across a country estate. It is the grisly man-to-wolf makeover of Benicio del Toro, following in the paw-prints of Lon Chaney Jr, that will pull in the popcorn-munchers. Del Toro plays Lawrence Talbot, an actor who can only be released from his lycanthropic curse by "someone who luffs heem", as a gypsy tarot reader puts it. Could that someone be Blunt's Gwen, his grieving sister-in-law, a woman given to lounging demurely on river banks in full funeral dress?
The odds aren't good on The Wolfman dislodging memories of the original, but then it's a miracle it got finished at all. Blunt was cast by the director Mark Romanek, who was then replaced by Joe Johnston (Jurassic Park III). There have been whispers that parts of the picture were shot without a director, but the actor is too diplomatic to say. "I try to disengage myself from that side of things," is the most she'll reveal.
Suspense in the picture arises from the ongoing battle between Del Toro and Anthony Hopkins, as Lawrence's father, to determine who can turn in the most demented performance. "Oh, they're both insane, aren't they?" says Blunt with a naughty laugh. We have a chuckle over Hopkins's choicest moment, when he breaks some shocking news to his son, then wanders over to the piano and starts tinkling away absently like one of the Fabulous Baker Boys. "I think we all took our cue from him. We tried our best not to add to the melodrama. Benicio and I even cut some of our dialogue because we thought it was more interesting to feel the space between the characters."
I tell her I'm shocked to hear that, since she and Del Toro don't have nearly enough time together before the fur starts flying. "Aww, that's cool that you think that," she coos. "But you're a film fuddy-duddy like me. You want all that human behaviour stuff. Everyone else, you see, just wants to get to the first bite." We agree that, on reflection, multiplex audiences probably won't be throwing their oversized soda cups at the screen and demanding greater emotional development. "But I knew what I was signing up for. Really I did."
Blunt announced recently that she didn't care if anyone thought she was a sell-out for making the movie. "People were, like, 'Why have you strayed away from independent films?' I thought, 'Give us a break! I've hardly done anything but independent films.' I think Benicio put it best. He said, 'C'mon, man. I like candy too, y'know?' That's how I feel. Why should you have to atone for making big movies?"
Blunt combines her enthusiasm with a determination to keep work from impinging on her private life. She lived for three years with the Canadian singer Michael Bublé, without whom the world's easy-listening stations would fall mercifully silent; her fiance is the actor John Krasinski, who stars in the US version of The Office. But she is adamant that dating other celebrities hasn't been an active choice. "It's just what's worked for me," she says. Wouldn't it be tricky for her to step out with a traffic warden? "Well, I don't know," she says, laughing. "It's to do with how the man feels, isn't it? Although this is a magical job, and I have that shared understanding with the person I'm with, it is still only what I do – it's not who I am. If you can make that distinction then you're in a good place."
She seems to have inherited level-headedness from her mother, a former actor who now teaches English as a foreign language. When I ask why she stopped acting before Blunt, the second of four children, had started school, she widens her eyes. "Why? Because she had four kids and a busy husband!" (Blunt's father is a criminal barrister.) She never saw her mother perform. "I wish I had. I hear she was wonderful." But she is at her most animated when discussing her upbringing in the not-too-shabby London suburb of Roehampton. "When you're one of four kids, it's a noisy, boisterous rabble. And so loving – we were always each other's biggest allies." As a child, she had a wild imagination. "I used to create elaborate games. There was one called 'Save Tigger', where my friend and I would hide my hamster, Tigger, under a pillow and pretend the room was going up in flames. Poor thing died a year later. Probably a heart attack."
For all this exuberance, Blunt was inhibited during childhood by a hereditary stutter. "It meant I didn't talk as much, so I guess I had more time to watch people and listen because I was intimidated by talking." The key to overcoming it arrived in the shape of acting. "I found it more helpful to speak in different accents when I did class plays because I didn't feel I was playing myself. I could disconnect from the fact that I, Emily, had a stutter. Now you can't shut me up."
Blunt has a pleasing appetite for oddity that should prevent her getting trapped on the studio treadmill. In her 2004 film debut, My Summer of Love, she and her co-star Nathalie Press created a study in teenage infatuation that was raw and intoxicating. Her mainstream breakthrough, The Devil Wears Prada, was a deeply conventional comedy that nevertheless provided an unbeatable example of her governing intelligence. All she had to do was play the claws-out PA to Meryl Streep's ice-queen editor. Pantomime stuff. Except that Blunt reasoned it would be more interesting to locate the character's inner pussycat: "I could've played her bitchier, but I thought there was something desperate about her. I felt sorry for her. And bitchy gets boring."
She underplayed winningly in Sunshine Cleaning, as a dope-smoking drop-out who helps her sister tidy up crime scenes. Even a foray into heritage cinema, The Young Victoria, was unorthodox, directed by a Canadian (Jean-Marc Vallée) who played music by Sigur Rós and the Rolling Stones on set to get his cast in the mood; Blunt gave an aching performance as the future queen, capturing a discontentment free of anachronism. She recently finished shooting The Adjustment Bureau with Matt Damon, a thriller adapted from a Philip K Dick story, as well as a remake of the spiky French comedy Wild Target, which reunites her with Bill Nighy (with whom Blunt worked on Gideon's Daughter, the BBC film that won her a Golden Globe). These are not the choices of a woman with a one-way ticket to blockbusterland.
For all that, she is not precious about her craft. In the middle of explaining how she approaches a role, she pulls herself up short. "Oh, I always feel so wanky talking about the process," she hisses. "It's like, 'Get a real job.'" But cinema is amazing, I point out, suddenly finding myself in the incongruous position of reassuring an award-winning, high-earning film star that her job is worth doing.
"Yeah, I agree," she says. "A movie can change your life. I used to be very British about it all: 'This is a lot of silliness, I should be doing something worthwhile.' Then this woman came up to me and said, 'I have to tell you, I had the worst day. My husband divorced me, my kid got expelled from school. Then I watched The Devil Wears Prada and I laughed my arse off!' And I thought how marvellous it was that a simple comedy could have that effect on someone."
The Wolfman is released on Friday
