Directed by Michael Apted, starring Dougray Scott, Kate Winslet, Jeremy Northam and Saffron Burrows.

One of the great battles of the Second World War remained a mystery for nearly 30 years. It was fought at Bletchley Park, a mansion in Buckinghamshire, where 10,000 men and women – mathematicians, translators and radio operators – cracked the Enigma code. This code was used by the German forces to relay messages and deciphering it is said to have shortened the war by two years. Without this triumph, D-Day would not have happened until at least 1946. There were 150 million different ways to configure a message using Enigma and to break it the Bletchley team created the first prototype of the modern computer. They were bound by secrecy after the war and it was only with the publication of a book in 1974 that the extent of their contribution to world peace and IT became known.

For those still alive, a bitter aftertaste was to come two years ago with the release of the US submarine film 'U-571', a movie which claimed that the American navy that had helped win the Battle of the Atlantic by capturing an Enigma machine from a sinking sub – all untrue. The machine was captured by a British navy team and later transported to the Home Counties. This film is an attempt to help set the record straight.

Based on Robert Harris' book of the same name and written by playwright Tom Stoppard, 'Enigma' focuses on Tom Jericho (Scott), a young mathematician who has returned to Bletchley after a nervous breakdown. Before "falling out of his pram" Jericho had cracked one variation of the Enigma code but you feel that in his mind this accomplishment pales alongside the fact that he had a dalliance with the babe of the base Claire Romilly (Burrows). It ended badly, leaving Jericho to pick up the pieces in a convalescent home and his return to duty is greeted with very loud murmurs about whether he's still up to the job. The answers his superiors feel won't be long in coming; the Germans have switched to a new variation of Enigma and Jericho must recrack the code – in the space of four days.

A cross between a TV drama about life during wartime and a tribute to the stiff upper lip movies of old, 'Enigma' is a character driven espionage thriller with a great double act from Scott as the unhinged code breaker and Winslet as Hester, his frumpy ally at Bletchley. The film eschews depicting the great acts of daring do in favour of the small parts that people played in winning the war and against this backdrop, director Michael Apted builds a mystery surrounding the disappearance of Jericho's former lover Clare. Has she just had enough of life during wartime and run away or is there a link between her vanishing and the appearance of smarmy intelligence man Wigram (brilliantly played by Jeremy Northam) at Bletchley?

There are no seven-minute shootouts, no explosions and no professions of everlasting love, instead Apted splits the plot between Jericho's attempt to get back into the code, his desperate search for Clare and his meeting of minds/burgeoning romance with Hester. The three strands link up in the last 20 minutes with Jericho discovering that he's only a pawn in a far bigger game, a game that stretches beyond the woodhuts of the Bletchley, the convoys of the North Atlantic and leads right to the stability of the Allied forces.

The chances of Enigma leading to queues at the box office are remote, it's too understated a film to get excited about, but for the great turns from Scott, Winslet and Northam and the timely reminder that the greatest acts of heroism are so often unsung, it deserves your attention.

Harry Guerin