'Did you know that Eric used to work here?' says Eric Lomax's widow, Patti. We're sitting in Creative Scotland's swish office suite at Waverley Gate, Edinburgh, also home to executive giants Microsoft and Amazon. Eric Lomax, who was born in Edinburgh in 1919 and who died last year aged 93, worked here as a sorting clerk and telegraph operator when the building housed the Post Office. When World War II broke out, he left his desk job to join the Royal Signal Corps. After the fall of Singapore in 1942, Lomax was captured by the Japanese and forced to work on the construction of the infamous Burma 'Death' Railway. What happened to Lomax in Thailand, how his experiences traumatised him, and how, with the support of his wife, Lomax enacted an extraordinary feat of reconciliation with his former captors and abusers is the subject of a new film starring Colin Firth and Nicole Kidman. Joined by the film's screenwriter Frank Cottrell Boyce, Patti Lomax is here to talk about the film, her late husband, and more.

'It's taken such a long time to get made,' Lomax says. 'The team who made it have become close friends, which is lovely. And to see it finalised, and so well, retaining the essence of the story, well, I'm delighted.'

A film adaptation was first mooted back in 1998, when Boyce, who had just finished work on another dramatisation of a true story, Hilary and Jackie, was given a copy of Lomax's 1995 memoir, also titled The Railway Man. 'We all met at the York Railway Museum, of course,' says Boyce (Lomax was a train enthusiast his whole life), and we hit it off. It's taken a long time to get here, but, looking back, I don't regret that. Colin Firth is older now – I can't imagine anyone else playing Eric. I thought we needed to make the film for Eric to see, but now I see it's a blessing that Eric isn't here to see it.'

'He wouldn't have seen it,' Lomax says. 'He would have thought it so convincing, it would have taken him right back. And he didn't want that; he was frightened of that.'

Although the film doesn't shy away from showing the horrors of war, the focus is less on the POW experience in Thailand and more on the effect it had on Lomax and his fellow veterans in the decades to follow. Both Lomax and Boyce feel this aspect of Eric's story has universal significance.

'Eric was very keen that people were made aware of combat stress,' says Lomax. 'That's what his book, and the film, are all about. It could be a warning to modern day people that combat stress can really be a problem, for the sufferer and for their families. Personally, I think Governments and politicians don't learn from history. Our government is so far behind. But the other message of the film is,' Lomax says, 'no matter how dire life is at any one point, it is possible to overcome that and move forward.'

General release from Fri 10 Jan.

The Railway Man (2013) Official Trailer