Rhona Mitra once saw a man headbutt another on the terraces at a Tottenham-Arsenal game. She never forgot the crunching sound of skull on nose. “I used to have such a fear about being head-butted,” she shudders. “I hate fighting. I don't know what I'd do if somebody attacked me. I'd probably run!” Which makes her role in Neil Marshall's relentless apocalyptic British thriller Doomsday all the more impressive. As an elite soldier, Major Eden Sinclair, she kicks, punches, bites and - yes - butts her way through a story that begins as a killer virus spreads north of the Border, forcing the Government to put a huge containment wall around Scotland.

For the British-born Mitra, it is an outstanding turn in a career that has threatened to go global for years. As Sinclair is sent back into the hot zone to find a cure, just think of Mel Gibson's Mad Max with more mascara. As Marshall puts it, the 31-year-old Mitra has a “hardness about her” that made her ideal casting, no doubt aided by a fabulous figure, courtesy of two months' training in pre-production with a bodybuilder. As a “sporty kid” (gymnastics, javelin, hockey, horse riding, you name it), pushing herself to peak condition came easily to her. “I'm one of those quite stocky troll-like people with good muscle memory!” she laughs.

In truth, with Indian and Irish heritage lending her an exotic beauty, Mitra is anything but troll-like. Enhanced by breast surgery, such is her physique that it is no surprise that she was employed as an early real-life incarnation of that CGI tomb raider Lara Croft. Still, while admitting that growing up between two brothers meant she was never “a girly-girl”, she is plagued by the question of whether she is a tomboy or not. “I've been told I'm very much a female. It's just the things I like to do. I don't mind getting my hands dirty. But I cook, I garden and I wear dresses! I just happen to like pulling reverse 180 handbrake turns as well.”

Doomsday allowed her to express her more masculine qualities freely, even if “there wasn't really that much on the page to play with as far as emotion is concerned”. Mitra clung to the detail that Sinclair was evacuated from Scotland as a child, leaving her mother behind. Shortly before she took the role, Mitra's own mother, Nora, died. “All that jumped off the page for me was this girl who was on a journey to find her mother. She's almost like a human tracking device and I found that really appealing.” Was it a cathartic experience? “Yeah, it really was. I feel like I'm talking to you as my therapist now but there was some closure in that for me.”

Born in North London, Mitra was a minx in her early years. “I was naughty. I really was, which for a second got a little bit out of control,” she admits. Doubtless it didn't help that her mother split from her father, a cosmetic surgeon, when she was young, but she was kicked out of a convent school when she was 13 for stealing Communion wine. “I think that was a bit of a faux pas,” she chuckles. “It's a typical teenage thing, trying to figure out what the hell was going on, and you act up when that happens.” She subsequently went to Roedean, was expelled, and ended up cramming for her exams in London.

After plumping for drama school, Mitra was cast as Lara Croft, long before Angelina Jolie played her on screen. She was hired to make public appearances at video game conventions, but the experience went way beyond her initial expectations. “I kind of was her!” she recalls. “I lived and breathed her for a couple of years. They had me write songs for her in character and record an album.” So well did she know the character, the producers of the original film even picked her brains for details. “I even knew what glass of wine [a merlot] she had for dinner!”

Although offers then came in, they weren't from Britain. “There was a lot of Lock, Stock... or Merchant Ivory stuff going on, and I'm not quintessential English-looking, so the roles were thin on the ground.” She took off to Los Angeles, initially to feature in the popular soap Party of Five. Since then, typified by her cameo as the “Bus Stop Bombshell” in the Farrelly brothers' comedy Stuck on You, her film roles have been largely restricted to sex kittens. “I'm not kidding myself,” she says. “I'm not Cate Blanchett. But I've been quite lucky [she cites working with Kevin Spacey on the death-row drama The Life of David Gale]. I've been able to be on the pitch and play, rather than sit on the subs' bench.”

Mitra has fared better on US television - playing Tara Wilson in The Practice and its spin-off show, Boston Legal - and her film profile looks set to soar after Doomsday. She has just completed a leading role in Underworld: Rise of the Lycans, a 12th-century-set prequel to the vampire franchise that starred Kate Beckinsale. “It's not actually filling Kate's shoes, which would have been insane,” she says. If it means staying in LA away from her family, at least she is not alone. In a long-term relationship with an actor - whom she won't name because “then it would be everybody else's and not just ours” - all Mitra will admit is that it's not someone she met on set. “I don't do that! Cardinal rule - don't sleep with someone you work with.” Smart girl, as well as a tough one.

Doomsday is released nationwide on May 9

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