I’ve long been fascinated by the story of Alan Turning. I first read Andrew Hodges’ book, on which The Imitation Game is based, sometime back in the late 80s or early 90s, although it was first published in 1983. Subsequently, I saw the TV version of Hugh Whitemore’s play, Breaking the Code, starring Derek Jacobi when it aired in 1996.

And I read widely around the subject, being fascinated with the subject of cryptography back in 1988 when I started studying maths at the University of Bath. As a scene early on in the film makes clear, everyone at Bletchley Park – or Station X as it was known – was told that they weren’t allowed to mention the work they’d been doing during the war. And so it was that well into the eighties and nineties, husbands and wives, sons and daughters, and grandchildren were only beginning to learn what their relatives had actually been doing during the war.

I can’t think that there are many people in the UK who are unaware of Alan Turing and Bletchley Park now. As well as several showings of Breaking the Code, we’ve had documentaries on BBC2 and Channel 4, as well as an ITV drama series based on the women who worked there. Then there was the big screen outing for Enigma (2001), based on the Robert Harris novel. More recently there was the best-selling Sinclair McKay book on the subject. And earlier this year, the Pet Shop Boys premiered a piece on Turing during the Proms.

Beyond that, there are more detailed accounts and personal reminiscences also published. Bletchley Park itself has been “saved” on more than one occasion, and is now a successful tourist attraction (Although there’s a rather nasty dispute between it’s trustees and the National Museum of Computing which is also based on the site. I’ve not heard what the latest outcome is, but it’s left many people very unhappy.)

I mention all of this to point out that I’m pretty familiar with the source material, and I was really looking forward to The Imitation Game.

And it’s a very good film. Like Breaking the Code before it, the film breaks up Turing’s life into three distinct parts – his time at Sherborne School, his time breaking the Enigma codes during WWII, and his time when he was arrested and charged with indecency as a gay man at a time when homosexuality was illegal in the UK.

The film moves between those times, trying to bring parallels between them. I always find that this can feel a bit forced. What we do in our younger lives doesn’t always presage what happens later. But the transitions work well. I would like to see a film where the story is told linearly though. It feels like this jumping around happens a little too much these days.

That said, I thought we could have seen more of Alex Lawther’s superb portrayal of a young Alan. The “odd fish” is treated horrendously, and his relationship with a friend – Christopher – is nicely drawn out. That said, they spent more time together in reality than the film shows.

The bulk of the film takes place during the war as Alan – now Benedict Cumberbatch – is enlisted to help break the Enigma code. While the allies had a machine – stolen by Poles who also did a lot of work trying to break Enigma – having the device wasn’t enough. The number of settings the machine has with different rotors, starting positions and plugboard settings mean that you’re left with a seemingly impossible hurdle.

The one thing the film doesn’t really get into, is exactly how Turing and his team were actually attempting to decode the intercepts. All we really get told is that each day there are new settings for the machines, and that coded messages are sent via Morse between the different German stations. The broadcasts could be heard quite easily by British listening stations, but they were left with meaningless letters.

So instead, all we really understand is that Turing decided that a big machine is the best way to cope with this, and exactly how the machine worked wasn’t really explained, except that it was using brute force to get to the right point.

This being a film, we need various scenes of tension, and if truth be told, I’m not sure things happened quite like that. At one point Charles Dance’s Commander Denniston marches in and unplugs the “bombe”. While Denniston was moved on by Churchill, this feels a little overly dramatic. Similarly, a moment when Turing seems to be seconds from being dismissed does not feel the way the British Army would have behaved. It’d have been terribly bureaucratic and not a scene of high tension. I’m not certain that the realisation of using a “crib” – a guessed bit of text at the start of a message, such as the weather – happened at a dance that our heroic protagonists raced back to their hut to try out.

But I’m probably being over pedantic. This is a film after all. Cumberbatch is excellent as Turning, and Keira Knightly’s Joan Clarke is well played. Matthew Goode is great as Hugh Alexander, and you wouldn’t want to mess with Mark Strong’s MI6 Chief, Stewart Menzies.

The film looks good, and scenes were filmed at the real Bletchley Park. Sometimes the budget does seem to constrain the film a little, although we do get enough to understand the death and misery that was being brought upon British cities and those in the North Atlantic as convoys brought much needed food and munitions. The film even tackled that thorny issue of what you do once you’ve broken the code, if you don’t want your enemy to realise that you have.

Director Morten Tyldum previously made the dark and rather funny Headhunters. This is very different, and I think he’s done a good job (interestingly, he’s due to next direct a version of one of my favourite William Gibson novels, Pattern Recognition). And I enjoyed Alexandre Desplat’s score which served the film well.

The film does ignore the other code-breaking that was going on at Bletchley, and the other codes and cyphers that also had to be tackled as the war progressed. And it doesn’t really get into his other computer work. That said, in voiceover we do hear about some of this.

I do have a slight problem with the end credits which claim that the breaking of the Enigma code was kept secret for fifty years. That’s obviously not true given the date that Turing’s biography was published. That said, it also recognises the wrongs that were done not just to Turing but to so many thousands of gay men over the years.

I did like the way the film ended though – which wasn’t quite what I was predicting. Overall, I think it’s an excellent film despite some of my reservations about how they told the story. Cumberbatch is excellent, and I hope that the film does well.