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Top secret notes by Alan Turing's codebreakers survived 70 years in Bletchley Park's walls

The handwritten workings were used to insulate the unheated huts where chilly Turing and his colleagues raced to break enemy codes.

The race to crack WW2 codes was dramatised in "The Imitation Game", but the film failed to mention how cold it was in Hut 6. Jack English

Notes handwritten by Alan Turing's fellow codebreakers in pencil and crayon survived nearly 70 years stuffed into the walls of the draughty huts where they worked to crack German military codes. Discovered in a renovation of the WW2-era Bletchley Park base, the unique notes will now go on display at the museum that stands where Turing and his colleagues made their crucial contributions to the war effort, while, it seems, shivering.

A chilly uninsulated hut is a far cry from the glamour of the Oscars, but the discovery is a reminder of the everyday struggles faced by the WW2 codebreakers portrayed in the Academy Award-nominated film " The Imitation Game". Not only did Turing and his colleagues work to crack German codes -- in the process pioneering aspects of computer science -- but they did it in crude conditions and under strict security rules.

"These are actual handwritten pieces of codebreaking -- workings out," says Bletchley Park's Director of Learning and Collections, Victoria Worpole. Among the rare finds are some notes that create a new mystery to be cracked: "There are some pieces of paperwork that we can't identify. Nobody seems to be able to work out what they are -- we've sent things off to GCHQ -- and there are a number of items that we've yet to understand properly. We're unveiling a mystery."

The top secret nature of the work going on at Bletchley Park meant notes and documents were ordered to be destroyed, but when things got nippy in Hut 6 it seems the chilly codebreakers were only thinking about keeping warm. With no insulation or heating in the freezing huts, wastepaper was scrumpled up and stuffed into holes in the walls and roof spaces, where the notes survived until they were discovered during a renovation in 2013.

When they were found, the notes were frozen to prevent further damage. They have now been thawed, cleaned and repaired and will go on display at the Bletchley Park museum next month. The museum and surrounding park have been returned to their 1940s design, largely using original materials.

It's not clear exactly who scribbled each item, but although they weren't written by Turing himself the papers do include techniques he devised. Among the notes are the only surviving examples of Banbury sheets, so-called because the stationery was printed in Banbury, Oxfordshire. Turing developed the Banburismus technique to take advantage of a mistake made by the Germans in the wheel design of the Enigma encryption machine.

That slip-up allowed Allied codebreakers to punch encrypted messages into two sheets of paper -- the Banbury sheets -- and then slide them over each other until they lined up, revealing a clue to the machine's rotor settings.

German code settings were changed each day, making this a daily challenge for the codebreakers. The race to decipher messages each day was dramatised in last year's "The Imitation Game", although the film does fictionalise many elements of both the process and the lives of Turing and his fellow codebreakers. The movie has been nominated for numerous Academy and BAFTA awards, including nominations for Benedict Cumberbatch as Turing and Keira Knightley as his colleague Joan Clarke.

Other more everyday 1940s items discovered during the restoration include pages of an Atlas, a fashion article from a magazine and fragments of a teapot.