A rare surviving example of an Enigma machine, used by the German military to send coded messages during the Second World War, is expected to fetch £70,000 at auction.

The machines were vital to the Nazi war effort but the Allies broke the codes - a feat said to have shortened the war by several years.

The work done to crack the codes by Alan Turing and fellow code-breakers at Bletchley Park was immortalised in the Benedict Cumberbatch film The Imitation Game.

The machine being offered for sale, which dates from 1943 and currently belongs to a European museum, will go under the hammer at Sotheby's in London today.

Few examples remain as many of the machines were destroyed by German forces as they retreated.