Thomas Hennessey & Claire Thomas 
Spooks the Unofficial History of MI5 From Agent Zig Zag to the D-Day Deception 1939-45 [EPUB ebook] 

The real history of MI5. ‘PO Box 500, London W2′; the nondescript address from behind which one of the world’s most famous Secret Services hid: MI5. This book, based on previously secret sources, lifts the lid on Britain’s Security Service in its battle against German espionage. During the Second World War, the Security Service, through brilliant officers such as Guy Liddell, Dick White and the fearsome spy-breaker, ‘Tin-eye’ Stephens, commandant of MI5’s interrogation centre, Camp 020, successfully ran the Double Cross (XX) system. XX agents such as the dynamic, womanising petty criminal ZIGZAG, the suave TRICYCLE and the aptly named CARELESS laid the basis for Operation FORTITUDE in which MI5’s agents BRUTUS and GARBO were central to the success of the greatest deception in modern military history: convincing Hitler that the D-Day landings in Normandy were an elaborate diversion to the ‘real’ Allied landings at Calais. It was MI5’s finest hour.