Anyone for whom a screening of the film The Great Escape is an annual Christmas tradition will know how strong a hold the myth of that escapade holds over the collective British imagination. But a myth is all it is. The old 1960s movie, with its star-studded cast performing stiff upper lip heroics, manages to turn a horrific tragedy and crime into an ‘Allo Allo’ style farce akin to Carry On Tunneling.

Now, the escape from the Stalag Luft III prisoner of war camp in Silesia (now Poland), and its terrifying reality, is in the news again. Almost exactly 80 years after the breakout a document has been discovered in the National Archives at Kew claiming that the escape mission was betrayed by two unnamed English traitors.

The mass murder of the camp’s escapees was a war crime

The previously unknown document was found in the National Archives during preparations for an exhibition on the escape. It was written by Flight Lt Desmond Plunkett, one of the lucky few prisoners who survived after being recaptured and held by the Gestapo for several months. 76 men who broke out of the camp in March 1944. Notoriously, fifty were shot in cold blood by the Gestapo on Hitler’s direct orders after they were rearrested.

Plunkett – loosely portrayed by the actor Donald Pleasance in the film – was the camp forger who made many of the fake ID documents used by the escapees. According to the historian Guy Walters, Plunkett may have become paranoid about planted traitors in the camp while he was held by the Gestapo. There is no other evidence, Walters said, that the Nazis had stool pigeons in Stalag Luft III. There is also no evidence to suggest Plunkett repeated his claims elsewhere when being debriefed after the war.

The mass murder of the camp’s escapees was a war crime, but was only tacked on as an afterthought at the end of John Sturges’s big screen version of the story. The film concentrates on the mainly fictional and sometimes farcical efforts of the Anglo-American cast as they dig their way to a brief breath of freedom.

Walters is rightly sceptical about Plunkett’s claim. He correctly points out that the escapees were caught in many different locations, and could not have been betrayed by British collaborators as most were recaptured as a result of their own errors.

In his book on the escape, The Real Great Escape, Walters correctly eviscerates Sturges’s movie myth that the escape was a jolly spiffing lark. He portrays the escape’s mastermind, Squadron Leader Roger Bushell (fictionalised as the character Roger Bartlett, played by Richard Attenborough in the film) as a fanatic criminally careless about the likely fatal consequences of his grand scheme.

Bushell was one of the fifty men shot after his recapture. He was well aware of the risks the prisoners ran: he had been captured and tortured by the Gestapo after a previous escape in 1941; the Czech family who had harboured him were shot. Consumed with hatred of the Nazis as a result, Bushell devised the plan for a mass breakout, ignoring explicit warnings by the Germans that ‘escaping was no longer a sport’ and that runaways would risk execution if they were caught.

Despite the ingenuity of their forged ID documents and fake uniforms, the escapees were ill-prepared for the harsh weather and the even harsher response by the Germans once they were out of the tunnel and clear of the wire. Most were quickly caught. Only three of them successfully made the ‘home run’ back to Blighty.

When news that the fifty men had been murdered broke in Britain, Foreign Secretary Anthony Eden publicly vowed vengeance. After the war the Gestapo officers who had shot the escapees were duly hunted down, tried, and hanged.

The Hollywood version of this story – most memorable for Steve McQueen’s (totally fictitious ) athletic exploits while motor cycle riding – is a prettifying falsification of a grim debacle. However heroic, it was more of a great disaster than a great escape.