It's hard to believe that Theresa Heskins has never seen iconic war movie The Great Escape.

But it means the director isn't burdened by "what we think we know" about the mass break out of Prisoners Of War from Stalag Luft III in March 1944.

Her dramatized version - Tom, Dick and Harry - is culled not from the 1963 film but from MOD files unsealed in 1972. The title springs from the prisoners' code names for the tunnels dug under the noses of their guards.

"I've avoided the film so I don't know how ours differs but we've gone back to the War Office archives and applied a bit of imagination to what words were said," she says.

Ham & High: Sam Craig and Nicholas Richardson in Tom, Dick and HarrySam Craig and Nicholas Richardson in Tom, Dick and Harry (Image: Andrew Billington)

"It's a story we all feel we know, but the first thing that struck us was it's not a strictly British story but a very international one. There were air crew from the Caribbean, Australia, Canada, Africa and several European countries. It's inspiring to learn about people from around the world coming together across national and language barriers to fight against something bigger than themselves - in this case fascism."

Heskins and co-writers Andrew Pollard and Michael Hugo were excited to read the original documents with their "amazing stamps and smell of old paper."

"We were really surprised that they explain in great detail how to break out of a prison camp including how to organise people into departments so that not everyone knew the whole plan, and signal and code systems for secrecy. Up to now it's been an individual's version of the story, but here was the official version of it. There had been breakouts of nine or ten before, but it was unusual to have a mass breakout. To try to get 200 people out was bold."

Ham & High: Dominic Thorburn in Tom Dick and HarryDominic Thorburn in Tom Dick and Harry (Image: Andrew Billington)

The camp was in an area that is now Poland, and Heskins says: "I always thought breaking out was the tricky thing, but when you see a map of occupied Europe you realise it's not just about digging the tunnel but about the clothing they needed to make you look like a businessmen on a train, or the forged documents to move around."

Numerous problems meant just 76 escaped with only three achieving a "home run". But their motivation was to divert German resources from the war effort.

"We spoke to serving members of the RAF who told us if you're captured it's your duty to try to escape. The POWs were not imprisoned civilians, they were still on active service. Escaping was their resistance. At one point there were 200,000 troops trying to track them down and if you have someone distracting German soldiers from the war that's useful."

Heskins who has previously directed hit productions of The Worst Witch and Around The World In 80 Days featuring a cast of eight playing 125 characters, says this is a story about 600 people told by nine actors.

"I like to put on stage something that should be impossible," she laughs. "This is the most epic thing I've done. The play starts in an aeroplane, goes underground and all across Europe. The challenge is to take all those facts and history and make it an exciting, vibrant, dynamic piece of theatre. It's very moving, there are lots of laughs and it's real edge of your seat stuff - theatre often isn't. We're asking audience members who are game to become some of the characters."

Ham & High: Andrius Gaučas, Sam Craig, Nicholas Richardson in Tom Dick and Harry which comes to Alexandra Palace Theatre in JulyAndrius Gaučas, Sam Craig, Nicholas Richardson in Tom Dick and Harry which comes to Alexandra Palace Theatre in July (Image: Andrew Billington)

One of the hardest things was striking the right tone between derring-do and genuine jeopardy.

"In that very first document there was an introduction by one of the POWs who said 'I hope if people tell the story in the future they will emphasise the spirit and ingenuity of the escapers.' I wanted to respect the people who went through this, and not diminish their privations, their restricted liberty and living conditions. Reading about how Red Cross parcels were the only way they survived because the food was so awful had added resonance when you think about what a valuable organisation they are right now.

"They used sport, the arts and their imagination to keep themselves sane. It's an inspiring example of human resilience in adversity. We are still telling that story which makes you think about what it stands for."

Tom, Dick and Harry runs from July 26-August 28 at Alexandra Palace Theatre.