The most remarkable fact about Operation Mincemeat is not that it went to plan, but that the Germans believed it.

In 1943, the Allies took a dead tramp from London and dropped him into the sea off southern Spain.

Welshman Glyndwr Michael had become the fake Major William Martin, who had drowned off Huelva and been discovered by the Spanish navy carrying secret letters identifying Greece for invasion by Allied forces (it was actually Sicily).

The faux officer was buried in the Andalucian city and the documents found their way on to Hitler’s desk in Berlin after a well-connected German spy working in the area picked up the communiqués.

The ploy saved thousands of lives as Hitler moved a Panzer division – 90,000 soldiers – to Greece.

When the Allies attacked Sicily, the island fell with a fraction of the casualties Britain feared. This helped to defeat Mussolini and, forced to confront an Allied invasion from the south, Hitler quelled his advances against the Soviets. The story was soon turned into the movie The Man Who Never Was.

Now, more than 60 years on, the forgotten man who helped to turn the war is to become the focus of a musical drama which fuses fantasy with reality in a style its creators compare to work by gritty dramatist Dennis Potter.

Paul Tibbey and Mark Sims, aka Balls In The Air Productions, have penned 11 original songs for what they call “a musical tragicomedy”, Dead In The Water.

Tibbey says the three-strong cast perform in a production which has an “accidental fable-like quality” rather than the suspense and thrill of espionage.

Glyndwr Michael, who’d had a terrible, solitary life at a time when the rest of the country was pulling together and bound by a spirit of defiance, only became important in death.

“We are coming at it from the point of view of this unwitting hero. We were interested in his story, about how he was completely unaware of his own importance, which is probably true of a lot of people. That makes it, in a certain sense, a universal story.

“Especially because lots of people suffered in the war but at the time didn’t realise the importance of their suffering.”

Dead In The Water sees Glyndwr Michael in his final hours at St Pancras Hospital.

He died of phosphorous poisoning, and as he is nursed through his final hours he becomes delusional and delirious.

He imagines he is being followed by an imaginary intelligence officer and has glimpses of his posthumous fate.

“It’s a ghost story in reverse,” says Tibbey. “It has slightly creepy, ghostly elements in a darkly comic way.”

The cast is small because the duo wrote it for small-scale touring-style theatre, but it “still has some of the epic sweep of a musical”, not least because its tunes are part-contemporary and part-1940s Irving Berlin.