What German spies? The British worked very hard to elminate them. From examining German records of the Abwehr, the Gestapo, ect... after the war historians have found virtually every spy Germany sent to Britian was found out and either 'turned' or hanged.

Even back in 1942 German intellegence agencys were routinely being fooled by the Allies. Deception operations such as Mincemeat in the Mediterranian or the maskrikovia that preceded the Soviet offensives were notably sucessfull vs the Germans. The Germans were less sucessfull than the Allies at breaking radio codes, and their air reconissance steadily reduced from 1942.