The Man Who Saved MI6: Thomas Joseph Kendrick. 

(a long-form post on the Greatest Spymaster you've never heard of)

Thomas Kendrick was one of the most senior spymasters in the British Secret Service during the 20th century. From pursuing Communist agents throughout Europe in the 1920s to monitoring Nazi spies in the 1930s, he served as the SIS head of station in Vienna.

Also in the '30s Ian Fleming, author of the James Bond novels, crossed paths with Spymaster Thomas Joseph Kendrick. The two men would work together again on the eavesdropping intelligence operation to bug the conversations of German Generals and POWs in WWII.

In Vienna, Kendrick encountered the British spy and later traitor, Kim Philby, and the Communist Edith Tudor-Hart; individuals whose actions would unsettle the British Secret Service for decades.

Kendrick had ventured into the perilous realm of German double agents and international espionage...

Nicknamed 'the elusive Englishman' by Hitler's Secret Service, his true identity confounded the Abwehr until his eventual capture. His arrest by the Gestapo and subsequent 'Soviet-style' interrogation triggered alarm in Britain, endangering the entire European network of British spies.

The Spymaster steadfastly refused to betray the SIS network or disclose any of their operations. Kendrick was abruptly expelled from Austria... but not before he had saved the lives of thousands of Austrian Jews.