'I started young but fame never came into it,' says The Finest Hours star Holliday Grainger

"Oh God, I would never be allowed to get too big for my boots!" shrieks the 27-year-old, who, despite the novel-like name, is keen to point out that she wasn't public-schooled and isn't posh.

"It's funny; I started young but fame never came into it," she says. "I think there's a big difference between being a working actor and being famous.

"I didn't even think I'd get this far in my career. I feel lucky to still be working and having the opportunity to aim for roles that I wasn't sure I'd ever have a chance of getting."

Since landing a part in comedy-drama series All Quiet On The Preston Front at just six years old, Grainger, who hails from Didsbury, Manchester, has gone on to enjoy success in TV, stage and film, with credits including Bonnie & Clyde, The Riot Club and Kenneth Branagh's big-screen adaptation of Cinderella.

However, not one to elude the task of perfecting an upper-class - often blonde - posho, it's her well-heeled performances in countless period pieces for which she's become known.

Traversing the eras, she has impressed in historical-fiction series The Borgias; Joe Wright's Anna Karenina; Mike Newell's Great Expectations and BBC One's Lady Chatterley's Lover. But it's her latest pouting, in 1950s Massachusetts, that's set to really turn industry heads.

Starring in Craig Gillespie's action-thriller The Finest Hours, Grainger plays Miriam, the headstrong and devoted fiancee of real-life hero Bernie Webber (Chris Pine of Star Trek fame) - the man who orchestrated one of the most daring rescue missions in the history of the US Coast Guard.

The film charts the destruction caused by a huge storm that struck New England in early 1952, wreaking havoc on everything caught in its path, including 500ft oil tankers the SS Pendleton and SS Fort Mercer.

Daniel Cluff, a Coast Guard officer in Chatham, Massachusetts - played by Eric Bana in the movie - dispatched his best men to aid in the rescue efforts, before ordering coxswain Webber to assemble a crew and take out the CG36500 (a 36ft, motorised wooden lifeboat) to look for survivors.

Packed with thrilling action sequences, the 3D motion picture is Disney's latest gallant effort to immortalise a story from archival footage and witness accounts, but perhaps most telling of the studio's involvement is the anchoring theme of the human spirit.

And someone who has plenty of courage, especially when it comes to speaking out on Bernie's safety, is Grainger's finger-wagging character.

"I loved playing Miriam because she has total surety, and such a strong sense of instinct that she's able to have the confidence to defy social conventions," explains the softly-spoken actress.

"She's the one that proposes to her boyfriend and she has the instinct to do what feels right - like walking into his place of work and speaking to his boss. But her journey throughout this movie is wavering on her understanding what her fiance's job entails, realising the fear and danger, and having to come to terms with that.

"She's going through the process of being vulnerable and then finds the bravery within, thinking, 'No, this feels right, so I can handle this'."

Telling the tale - and making it look spectacular - Grainger believes was down to director Gillespie's ability to cast authentic characters.

"This is an epic action movie which could have very easily been overly dramatised, but Craig was really trying to reign in Bernie and Miriam's relationship, so it always felt real. He was going for that composed stoicism which is so appropriate for people living in a small fishing village with such harsh environmental conditions; there's a kind of a strength and composure that you must have in order to survive, and he's managed to capture that atmosphere in the film.

"Part of the reason that Chris and I fell so in love with Bernie and Miriam is because of the fact that, in real life, they genuinely met on the phone," she adds. "They were talking for four months before they even met each other, which is just unheard of now."

A poster girl for the genre, Grainger's youthful features make for a bona fide guise. While today she's girl-next-door: English rose, fresh-faced, natural and understated in a simple knit and skirt combo, her doll-like looks offer up the ideal base for the hair, make up and costume department.

"I liked the level of ladylikeness," she says of her character's 1950s style. "I love the fact that in most of this movie, Miriam has just come from work, so she's very 'officed' and done."

But running around the shore in a storm, wearing a dress and heels, has its pitfalls.

"When I came on [set], the guys had already been shooting for a couple of months and they'd been freezing in the studio in this cold water, so the producers had managed to find military-grade heated wetsuits for them.

"By my second day on the coast, I was so cold that I managed to squeeze one of them under the dress! I had my own little controls dangling down by my knees," she confesses with a grin.

Aside from keeping warm, another challenge was perfecting the Boston accent, which Grainger claims was "the most consuming bit of prep".

"The only American accent I'd done before was Texas. I didn't even have an ear for Massachusetts - I kind of knew the Boston South-y gangster accent but that wasn't right, so it took a long time before I could even start to produce it."

Unfazed by the task and pragmatic in her response, it's little wonder Grainger is a contender in Hollywood's surge of young talent, next joining an all-star cast as Maria in Tulip Fever, a 17th-century film directed by Justin Chadwick and adapted from a British novel.

But, she admits, being in her late 20s often sees her caught between the lines.

"I guess it's quite an exciting age, because a lot of the deeper, grittier, fuller roles are often for older women, but I do feel like I'm caught in a kind of... I can still do the early 20s, but then a lot of the time, I'm like, 'How am I playing a mother again?'" she explains.

Will more accessible projects for the rising star, who currently splits her time between London and Manchester, mean a move to LA?

"I love LA; the lifestyle feels so easy and I definitely see myself spending periods over there," Grainger begins. "But whenever I'm in the sun too much, I just crave a snowy, European city.

"I want a drizzly Parisian coffee shop or something!"

The Finest Hours opens in cinemas tomorrow