It was a diagnosis remote from the truth.
They had assigned an a priori probability of zero to Enigma decryption, and no weight of evidence sufficed to increase it.
It was a blunder, but one easy to make when the implications were so shattering.
At Bletchley, where it was explained to Hut 8 that decrypts could not in future be exploited so easily, there was nothing to do but to cross their fingers.
The Bombe method, which was central to the system, hung upon a single thread.
If, to be on the safe side, the Germans had gone over to a double encipherment of every message, then there would have been no more cribs, and all would have been lost.
At any time, the mere suspicion that something had gone wrong might stimulate such a change. They walked on a knife-edge.
From mid-June 1941, the Admiralty caught on to the idea that messages which contained information derived exclusively from Enigma decryption (normally until then, from Luftwaffe Enigma) should go out as ULTRA SECRET on special one-time pads.
The other services also began to adapt, setting up Special Liaison Units, attached to headquarters in the field and around the Empire, charged with the reception and control of Bletchley information.