Noomi Rapace: "It was almost like we put a lid on it and slowly opened during the film"

Master an accent, and you've mastered acting. It's served Toni Collette, Christian Bale, Saoirse Ronan and Hugh Laurie well, as audible proof of their technical skills.

For other greats (Dick Van Dyke and Keanu Reeves, please stand up), it's not their strongest suit to play.

Indeed, Tom Hardy is an indisputably fine actor - as proved in The Dark Knight Rises, Tinker Tailor Soldier Spy and Lawless - but even he admits adopting a Russian accent in his new film Child 44 was challenge. Certainly, you know you're in trouble when you view Sesame Street as a dialect resource.

"I watched Sesame Street because the Count speaks just like it," he says. "I couldn't get it off the ground at any point, and thought that's the best I could do."

We get the distinct impression it's not an accent, nor perhaps a film, he's proud to show off. With his newly shorn hair and full beard downplaying his Hollywood looks, he's pleasant enough, but the proverbial gun to his head is palpable. Earlier on in the day, he cancels our planned meet with little notice, and his second attempt at the London premiere is hardly co-operative. Leaving his hotel for the event, he walked straight past the car charged with delivering him to Leicester Square on time and arrived at the venue on foot, late. That's one way of minimising your promo-window accidentally-on-purpose.

Co-star Noomi Rapace, is the opposite: full of enthusiasm about the thriller and keen to grant us an audience. Her casting came via the film's producer Ridley Scott, who directed her in sci-fi blockbuster Prometheus.

"I loved working with him and trust his opinions," she star says. "After I spoke to him about it, I read the full story and I loved it."

Strong-willed characters
No stranger to taking on varied roles, from Scott's strong-willed scientist Elizabeth Shaw to rebel heroine Lisbeth Salander in The Girl With The Dragon Tattoo, she bleached her hair and eyebrows light blonde to adopt the guise of Raisa. She's a downtrodden wife in the grip of Stalin's communist regime, who joins husband Leo Demidov, played by Hardy, in the hunt for a child killer. Rapace's commitment began months before production began, the Swedish native explains.

"I watched Russian films, I read Russian books and plays, Tolstoy, Dostoyevsky," she says, now returned to her natural colour. "I filled myself up with information, and I had it in my spine when we were filming. You don't need to think about the history because you have it in your system, and then the scenes of the day take over."

Based on the first of a trilogy of novels by Tom Rob-Smith, Child 44 is ostensibly about the tense hunt for a child killer, but it also serves as a Dr Zhivago-style historical drama about the relationship between the couple.

"They've been married for eight years, but they don't know each other," says Noomi. "They're in this society where everyone is an emotional prisoner, where you can't allow yourself to be yourself, so they're both trapped. So while they go on this journey to find the killer, they discover themselves and each other. It's almost like a love story in reverse."

Fast friends
Hardy and Rapace are fast friends, to the point where they were cornered into denying romantic involvement (for the record, Hardy is now married with an eight-year-old son while mother-of-one Rapace is divorced). Their existing relationship was a resource for the film, their second project together after crime drama The Drop.

"We came straight from doing that shoot so we had a body of work in us already - it was almost like we put a lid on it and slowly opened during the film."

 Russia, however, failed to see the human essence of the film in the same way that North Korea didn't get the 'humour' of The Interview; the film has been banned there, with Hardy moved enough to comment.

"I really like Russia, so I’m upset," he says. "I have a huge respect for Russian people, art, culture and history. I hope it doesn’t affect me going over there and meeting people."

We doubt it will, not least because he's lining up a number of box-office friendly movies. While Rapace prepares to reprise her role in Prometheus 2, Hardy is gearing up for the reboot of Mad Max, his role of both Kray twins in Legend, and The Revenant, also starring Domnhall Gleeson.

Clearly not one to shy away from challenges, he's even undertaken a musical in the form of London Road. How proficient is he at singing, we wonder?

"I did some rap when I was a kid but I’m somebody’s dad now so it wouldn’t be too cool to crack that out," he grins (yes, videos are on YouTube). "I'm not really drawn towards singing and musicals and that stuff. But I had a crack at it because Rocketman movie is down the line and I thought I would try and open my mouth in that way."

Ah yes, his representation of Elton John in the biopic. Perhaps not the smoothest way to get Russians back on side...

Child 44 is out now