Intellectual Property

Britain were under somewhat of a "martial law" during World War II. Considering Alan Turing were employed by the British Government and worked on a classified project, it would be assumed that all rights to intellectual property developed in duration of the project will fully be under control of the British Government. The existence of Christopher were kept secret for almost 50 years before being made public

During time of peace, actions like these from a federal government would be deemed unethical and corrupt, however in times of war were millions could die, it would be acceptable. 

Fortunately, all credits were eventually given to Alan Turing and collaborators at the end of the movie.