They simply called it the cryptography school or code breaking school no big fancy code name like the manhatan project.
But it was the material they got from the enigma code break that was given a code name it was called Ultra.
And the information could not be used for combat operations unless they could find a way to make it look like the information came from other more reasonable sources to the germans. Because the Germans had to be kept in the dark that the info was from there own coded radio trafic using the Enigma machine. What is funny is that in the US the material from the Breaking of the Japanese Naval code during world war II by the navy was also called Ultra.

The only thing I can remember that the British ever used subtravuge to hide something in their own country was the fuel pumping station for the Normandy Beach Head. The station was on the coast and pumped fuel through a small pipeline run across the English channel during the invasion. The Pumping station looked like a simple Icecream parlor of the day from the air but if you looked at it from the ground it stood out like a sour thumb. All the locals new what it was but in Typical British Manner simply did not talk about it to avoid the location being discoved by the Germans.

Most spys the Germans had in Britain we rounded up and given a choice turn and only send what we tell you to send of be deal with as a spy in the manners allowed by the Geneva convention. Basically you can be executed without due process is found to be a spy. That is why if a German soldier ever had to do anything behind enemy lines they wore their uniforms under the civilian cloths so they could not be condemned as spy's. Because if you are on a battlefield in a military uniform you are to be treated as a POW under the Geneva Convention and can not be executed without sufficient cause as prescribed.