The "man who never was", was a dead body with documents, planted by the British Government to fool Germany into thinking that there would be an attack in a different site to their invasion plans.
This will be an exception to writing letters home to his mother. As he was dead, it will be a letter from the British Government.

Dear Mrs X,
                    Our Government thanks you for your son's service to his country. His successful mission was of great importance to the war effort. His supreme effort will not be forgotten. 

Ewen E. S. Montagu