As Colin Firth brings Eric Lomax's courageous true story to the big screen, the Oscar-winning actor tells Sophie Herdman about meeting The Railway Man writer before his death, how he couldn't help falling in love with trains and why he doesn't feel very British.

He's played some of Britain's most celebrated characters, from Jane Austen's timeless heart-throb Mr Darcy in the BBC's well-loved adaptation of Pride And Prejudice and modern-day love interest Mark Darcy in Bridget Jones's Diary, to King George VI in The King's Speech - but Colin Firth finds the idea of being the archetypal British gent a little odd.

"I've never felt entirely English, really," says the actor who received an Academy Award in 2011 for his portrayal of the historic king and his secret struggle with a stammer.

In fact Firth's had a culturally diverse life - his parents were brought up in India, as a child he lived in Nigeria and, since 1997, he's been married to Italian creative director Livia Giuggioli.

"I've never felt I quite slotted in perfectly. Perhaps that's why it [acting] all happened," he says, looking particularly British in a black jacket, smart white shirt and square-framed glasses.

"You put on a mask, an identity, and it fits all too well. I might be like one of those ex-patriots who seem more British than the people who actually live in Britain."

Then he starts to chuckle.

"I might have taken on something of a pastiche, while all the real English people have moved on and don't walk and talk like that at all."

His latest film, The Railway Man, will do little to shake this British label.

It's powerful stuff, telling the true story of Eric Lomax, an Edinburgh-born engineer and British Army officer who, during World War Two, was captured and tortured at the hands of the Japanese, while being forced to help build the infamous 'Death Railway'.

Eric, played by Firth, was eventually set free but suffered from post-traumatic stress disorder, which he later described in his autobiography, The Railway Man, originally released in 1995.

While Eric had a dark past, there was one thing that always made him smile - trains. From a young age he was fascinated with the railway.

"He had such a twinkle when he talked about it," notes Firth of Eric, who passed away, aged 93, in 2012.

Such was Eric's love of trains that when his book was reprinted in time for the film's release, he asked for just one correction to be made.

"A detail about the brass fittings on one of the engines," explains Firth. "It wasn't about the big stuff, it wasn't about anything that you or I would think was important, but it was very important to him."

As it turns out, Eric's obsession with trains was infectious and while reading his book, Firth found himself getting excited about engines too.

"I quite like trains anyway," he admits. "But he imparted such delight in a world when these things were still new, it made me envy the steam age, how magnificent these monstrous machines were. So the books I got for research weren't just about World War Two, I started to get books about trains too."

Firth doesn't collect anything himself ("But I completely admire that passion and devotion to something," he says), though he does have a hobby - playing guitars.

"I'm not very good. I don't think I'm even good enough to discuss the matter but I do love guitars, I fetishise them as objects," he reveals.

"I play just as an excuse to hold one, which I could probably do for hours. Not like an air guitar, just something to cuddle. I think they're beautiful."

His role in The Railway Man isn't the first time he's portrayed a man who's been at war. In 1988, he played Falklands veteran Robert Lawrence in Tumbledown.

"Robert was able to share stuff with me, so to that extent I had some experience of trying to understand something that is beyond my experience," says the actor.

Understanding Eric's experience, however, was more of a challenge.

"What he went through was so immense, so long ago, and his story has covered many more years than I have lived," the 53-year-old says.

Firth spent time with Eric before and during filming, and admits that the man he met wasn't quite what he'd been expecting. "I was all ready to fall into that trap of thinking, 'Ok, he's 92, speak up a bit and slow down,' but there was no need for it at all," he explains. "There was nothing wrong with his faculties. They were a lot better than mine - he could have been 20.

"I was meeting a man whose story was still going on, even in his nineties. It didn't stop with the end of World War Two, it didn't end when he wrote his book. It was still unfolding."

It wasn't just the time spent as a prisoner of war that damaged Eric, Firth notes, but also the years when, upon his return, he couldn't bring himself to talk about what he'd been through.

"We're telling a story that is to do with the power of story-telling, and how detrimental it is not to be able to tell your story, even to the people closest to you," adds Firth.

Once Eric started to describe the ordeals to his wife Patti (played by Nicole Kidman), who he met years after the war and married in 1983, healing began.

"We had the job of somehow continuing the story-telling process," says Firth. "So there was a sense of responsibility, pressure and privilege."

Extra time - Colin Firth

:: Colin Firth was born in Hampshire on September 10, 1960.

:: His parents were academics and he is the eldest of three children. His sister, Kate, is a stage actress and voice coach who worked with him on The King's Speech, and his brother, Jonathan, is also an actor.

:: He has two school-age sons with his wife Livia Giuggioli, called Luca and Matteo, and an older son, William, from a previous relationship.

:: Following his performance in A Single Man, in 2010 he received his first Oscar nomination and a Bafta win. The following year, he took home both gongs for his role in The King's Speech, and was awarded a CBE for services to drama.

:: He's a keen activist and in 2009 was awarded the Bafta Britannia Humanitarian Award for his work supporting Survival International and Oxfam.

:: The Railway Man is released on Friday, January 10