During WWII, England sent thousands of Nazi POWs to stately homes where they could eat, drink, play pool, and even keep servants. 

They had no idea that all of the rooms were bugged and many of their fellow ‘prisoners’ were actually Germans of Jewish origin who became spies for the British after being forced out of their homeland. 

The information gained was so important that the government gave them an unlimited budget. 

(Source, Source 2, Source 3)