Once the embassy had been tipped off that there was a spy operating in the facility in early 1944, Bazna found it increasingly difficult to gather intelligence. The British Field Office had warned the embassy of a security leak. Bazna forwarded the document to the Germans. The warning had come to Churchill from Roosevelt, who obtained the information given by a defector to the US. A new alarm system in the British Embassy now required Bazna to remove a fuse whenever he wanted to look in the ambassador's safe.