In Northern Poland in 1940, at the Nazi war camp Stalag XX-A, two men struck up an unlikely friendship that was to lead to one of the most brazen and remarkable wartime escape stories ever told.

Antony Coulthard (nicknamed ‘The Professor’) was the privately educated son of wealthy parents with a first-class honours degree in modern languages from Oxford. The other man, Fred Foster, was the son of a bricklayer from Nottinghamshire who had left school aged 14.

Held in captivity, this seemingly mismatched pair would bond together and hatch a risky plan: they would perfect their German, forge travel documents, disguise themselves as travelling salesmen – and simply walk out of the camp.

Their journey would take them into the very heart of the Third Reich, stopping en route to sightsee and drink at a notorious Nazi watering hole.

‘It was a clever strategy, but a high-risk one. Success or failure would depend entirely on one thing: their ability to pass themselves off as native German speakers. The weight of this rested largely on Antony, whose fluency would be their passport to freedom. The serious challenge was to get Fred’s skills up to a level where he could just about pass muster during the time required. It would be, as Fred put it, “one big bluff”.’

What happened next is both heart-stopping and tragic.