“I’m forced to the unlikely conclusion that I’ve fallen in love,” reports Eric Lomax (Colin Firth) to his fellow officers at a veterans club in Berwick-upon-Tweed in 1980, some three and a half decades after he survived the terrors of being a prisoner of war at the hands of the Japanese along the infamous Burma Railway. Patti, the unlikely object of his affection, is played by the beautiful Nicole Kidman. The pairing is not as improbable as that in Frankie and Johnny (1991), where we were expected to believe in Al Pacino and Michelle Pfeiffer as lonely souls who had never had any luck snaring lovers before. That is one of the inherent problems when good scripts about dowdy characters attract larger-than-life stars: the story doesn’t necessarily play out as intended on the page. Still, we have been suspending our disbelief for nearly a hundred years.

Australian director Jonathan Teplitzky’s The Railway Man (in national release 26 December) is a sharp swerve from his previous feature Burning Man (2011). The earlier film was a complex, very contemporary Australian drama, while the new one, set in England and Thailand and based on Lomax’s real-life autobiography, resembles nothing so much as a Merchant Ivory film.

Lomax’s fellow survivors – and Lomax himself, until he finds love late in life – appear to while away their days at the veterans club. It is there that Patti arrives, determined to find clues that might shed light on her husband’s frozenness, which might today be labelled post-traumatic stress disorder. “I want to know what happened to Eric,” Patti says to Lomax’s old friend Finlay (Stellan Skarsgård). “He gets as far as the fall of Singapore and then he shuts down. And then he won’t – he won’t talk about the railway.”

“They had him for a little while,” Finlay tells Patti. “A week or so. We did our best to put him back together again. But we knew it wasn’t over.” Finlay relates to her the story in detail; the film goes into extended flashback, with Lomax played by a younger actor (Jeremy Irvine). Lomax was in Singapore with the British Army when it fell to the Japanese in February 1942 and was one of thousands of soldiers captured and marched to Thailand. In the camp at Kanchanaburi, he helped other men jerry-build a radio from scrounged electrical parts. In the film, its use is relatively benign: it’s only a receiver, not any kind of transmitter, and all the men really do with it is listen furtively to news from afar. But it gives them hope. “The Russians have taken Stalingrad,” Lomax tells a senior officer, himself traumatised and broken by the Japanese. “Got them on the run, sir.” When the Japanese find the radio, Lomax takes the brunt of the blame and is tortured to the brink of death.

In the 1980s, a tragic event compels Lomax, supported by Patti, to go back to Thailand, where he confronts one of his torturers, Takashi Nagase (played by Tanroh Ishida as a young man, Hiroyuki Sanada later). Nagase has funded the building of a Buddhist temple, in part to atone for his acts during the war. There’s a Burma Railway museum there, too, where Nagase takes Western tour groups. In Lomax’s eyes, Nagase is a torturer who has reinvented himself as a tour guide and translator. For a moment, the lid lifts off the repressed decades.

“I will not forget the tragedy of war,” says a frightened Nagase.

“The what?” says Lomax.

“The tragedy.”

“No, this wasn’t a tragedy,” explodes Lomax. “This was a crime. You’re a criminal. You were an intelligent, educated man. And you did nothing.”

(In real life, Lomax and Nagase experienced a kind of reconciliation, and were friends for the rest of their lives. Nagase died in 2011 and Lomax in 2012, both at the age of 93. Nagase had become a devout Buddhist and made more than 100 “missions of atonement” to the River Kwai.)

Frank Cottrell Boyce has written some excellent screenplays, including 24 Hour Party People, a marvel of a movie directed by Michael Winterbottom. The Railway Man is no disgrace. It’s sincere and tight, if mawkish here and there. And yet, though it gets a little saccharine, its tale is genuinely moving.

Lomax seems to have sublimated all his trauma into that classic English eccentricity, trainspotting. After the war, Finlay tells Patti, “[Lomax] went round and round the country collecting railway memorabilia. His whole life has been trains.” (In the film, Patti and Eric’s first meeting is a roundabout result of his Asperger’s-like obsession with timetables.)

At the beginning of the film, a distraught Lomax recites an odd, apparently self-penned poem, part doggerel, part nursery rhyme, that includes the lines:

Count not, waste not the hours on the clock.
Behold, I stand at the door and knock.

For Lomax, his obsession has kept in check a world of chaos, as presented to him by the events on the Burma Railway. But at some point he’ll have to step through that door, in order to arrive somewhere new.

“We don’t live,” Finlay tells Patti, explaining why all the men are so stitched up, decades after the war. “We’re miming in the choir. We can’t love. We can’t sleep.” In The Railway Man, Teplitzky is interested in investigating the process by which a mute man might move from miming to singing.