GCHQ and it’s American counterparts were more interested in deceiving the Soviets into believing that they hadn’t been able to break a type of cipher unrelated to Enigma, namely the pseudo-Vernam Ciphers as embodied by Tunny/Lorenz/* Geheimschreiber* for transmitting stream-enciphered teleprinter traffic (as decoded by Colossus). Enigma was trivial by comparison and it’s insecurity was known to the USSR.