A team of Canadian researchers claimed earlier this month that the code contained details of German tank movements which had been sent by a British soldier.
However, Michael Smith, a trustee of Bletchley Park, said the claims were "nonsense". He said the Canadian academics had used a World War 1 code from the First World War as the basis of their research.
He said: "The idea that a World War 1 code would have been used during the second world war is just silly. It wouldn't have been used because it would have been well known to the Gemans and insecure.
"More to the point you don't have to take my word for it. GCHQ have looked at it. They are very good at diagnosing codes and ciphers as the people at Bletchley Park were in the war. They can be pretty specific about it."