For Frank Cottrell Boyce and Andy Paterson, finding the right way to tell the story was the first and most difficult task. Characters who can’t or won’t communicate aren’t easy to put on screen. Lomax had written that ‘the ordinary former Far East POW has probably never talked to anyone about his experiences. The victim of torture most certainly does not talk.’

Their first meetings with Lomax were only two years after the book was published. “We realised later that we’d come into a story that was still unfolding. Suddenly a man who had blocked out the world for decades was a public figure, expected to share his most intimate secrets.”

“Initially we had expected to tell the whole story, exactly as it happened in the book. But when, for example, Eric talked about the aftermath of the meeting with Nagase, how somehow ‘all the pain just went away’, we realised even he didn’t yet fully understand how that had happened.”

Producer Bill Curbishley believes “the book has quite rightly been called a classic of autobiography. But Patti is barely mentioned. We suspected that was hurtful to her, but she would never say it. She’s a wonderful, loyal, no-nonsense lady, not given to self-pity. For a long time she refused to accept that her story mattered at all. How could her suffering compare to what those men went through on the railway? Yet, as Colin Firth put it much later, there is no story without Patti. She was the miracle in Eric’s life.”

There was no doubt that Lomax spent decades “nursing himself to sleep” with thoughts of revenge. Jonathan Teplitzky recalls sitting, later, with Eric and Colin Firth. “Colin asked him if he would have killed Nagase and Eric immediately said ‘Yes’. He had clearly thought it through many times.” The filmmakers needed to understand how Lomax could have made the journey from wanting “to cage, to beat, to drown” his former tormentor to a place of relative peace.

Crucial insights would come from Helen Bamber, who had been a key figure in Eric’s rehabilitation. Bamber had entered the Belsen concentration camp at the age of nineteen and stayed there for 2 1/2 years. After working with Amnesty, she founded the Medical Foundation for Victims of Torture. Eric says his first meeting with her was “like walking through a door into an unexplored world, of caring and special understanding. She learned as a girl in Belsen the importance of allowing people to tell what had been done to them; the power of listening to their testimony and of giving people the recognition that their experience deserves.”