A manuscript handwritten by Bletchley Park codebreaker Alan Turing could fetch more than £1 million at auction.

The 56-page document, which is full of mathematical notes, is thought to be have been written by Turing during World War Two.

It will be sold at Bonhams auction house, New York on April 13.

Turing spent his early years in Upper Maze Hill, St Leonards. In 2012 a blue plaque was unveiled at the house on what would have been his 100th birthday.

He went to day school locally in Charles Road before going to Sherborne School, Dorset.

He began work as an academic but after the outbreak of war he started work at the top secret code breaking unit at Bletchley Park, near Milton Keynes.

It was there he broke the Nazis’ enigma communication code, which is thought to have shortened the war by two years and saved millions of lives.

He is also widely regarded as the father of modern computing.

Evidence in the manuscript dates it to 1942 when he would have been at Bletchley Park.

It was among papers left to his friend and fellow mathematician Robin Gandy after Turing is believed to have taken his own life in 1954.

His death came after he was sentenced to chemical castration after prosecution for being gay.

Gandy gave most of the manuscripts to Turing’s old college, King’s College, Cambridge, but retained the notebook because amid Turing’s work he had written his dream journal.

In a note at the beginning of the manuscript, Gandy put : “It seems a suitable disguise to write in between these notes of Alan’s on notation, but possibly a little sinister; a dead father figure, some of whose thoughts I most completely inherited.”

The notebook remained hidden until Gandy’s death in 1995 and has since been kept by his family. In recent years it has been with a private collector.

Last year a film called The Imitation Game, which is based on a book of Turing’s life, was released.

Leading Turing scholar Andrew Hodges said: “Alan Turing was parsimonious with his words and everything from his pen has special value.

“This shines extra light on how, even when he was enmeshed in great world events, he remained committed to free-thinking work in pure mathematics.”