Cracking the code: an interview with The Imitation Game director Morten Tyldum

“He’s one of those big unsung heroes in history and I feel very grateful to be allowed to tell his story,” says Tyldum, who first attracted worldwide attention with the grisly but frequently funny thriller Headhunters. He was, however, determined to follow it up with something entirely different.

“Headhunters was a breakthrough film for me, internationally,” the director says, “and I got offered a lot of scripts from Hollywood — a lot of heightened hero movies. But then this script came along and I became obsessed with it because it was such a tremendous story. Sometimes you read something and you have to read more and more about the background… This is such a beautiful story because it’s really about how important it is to have people who think differently, who are not just being the norm. I thought it was a really important story to tell.”

His enthusiasm proved infectious. “I got the exact cast I wanted. I was already a big fan of Benedict and he said yes immediately. Behind the camera, too. Billy Goldenberg had just won an Oscar for Argo and is one of the hottest editors in Hollywood: he came on board immediately. Alexandre Desplat agreed to write the music, even though he didn’t really have time, because he loved the project. Everybody wanted to come on board, so it was one of those special experiences.”

Cumberbatch gives one of his best performances as the awkward, socially inept but brilliant mathematician. “He just gave and gave,” says Tyldum. “We’re both perfectionists and we both like to push things, so that was why I’m so proud of the result and of how good he is.” The rest of the male cast — including Matthew Goode, Mark Strong, Charles Dance and Rory Kinnear — is equally strong. And Spanish cinematographer Oscar Faura bathes each of the film’s three time periods — the 1930s, the war and the early 1950s — in a distinctive light.

But the real revelation is Keira Knightley, who gives a low-key but utterly convincing performance as Joan Clarke, another mathematical genius on a par with Turing but battling a world where a woman’s war role is seen as being primarily secretarial. “Keira is a phenomenal actress,” says the director. “She really wanted this part and I think she can relate to a lot of the qualities — about being an intelligent woman who is not always appreciated for it.”

The story of cracking the Enigma code has, of course, been told before — in the 2001 film Enigma, which managed to leave out Turing altogether. The Imitation Game, by contrast, is as much Turing’s story as it is a film about code-breaking. Based on a book by Andrew Hodges, himself a leading mathematician, and with a screenplay by Graham Moore, it follows Turing from schooldays in the 1930s via Bletchley Park to post-war Manchester, where he is arrested for propositioning a man in a pub. Homosexuality was then an imprisonable offence and Turing was duly jailed in 1952. It broke him and he committed suicide two years later.

In 2009, following an internet campaign, Gordon Brown made an official public apology on behalf of the British government for “the appalling way he was treated”. The Queen granted him a posthumous pardon on Christmas Eve, 2013.