In the 1950s Ultra (the code name for the massive British project that regularly decrypted German radio communications) was still a state secret. The reasons for maintaining this secrecy long after the end of the war aren't fully known, but German encryption devices (of which Enigma was one) had been sold to many countries around the world and Britain probably wanted to preserve the possibility of reading their secret communications if necessary (the machines used for this had been destroyed and the personnel disbursed, so this wasn't something Britain was still doing at this point).

So it would not have been possible for anyone to weigh in on Turing's behalf and publicly point out how instrumental he had been in helping to win the war. But surely someone like Churchill (who was still alive) could have interceded behind the scenes. Truly shameful that nobody did.