Blunt and Operation Triplex

In his memoir's book written in Moscow - then the capital of the Soviet Union - Harold Adrian Russel («Kim») Philby reveals: «There were also sophisticated techniques of opening foreign diplomatic bags. This method could not be used against the enemy directly, since German and Italians bags did not passed through British territory. But the bags of the neutral states and the minor allies, such as the Poles and the Czechs, were fair game». And he adds: «(...) the diplomatic correspondence of the South American states, of the Spaniards and Portuguese's, of the Czechs, Poles, Greeks, Yugoslavs and many others, was regularly subjected to scrutiny».

After research, I came to the conclusion that the man in charge of the Portuguese bag was Anthony Frederick Blunt, a MI5 official and one of the Ring of Five communist moles in the British intelligence élite, later Professor of the History of Art at the University of London, director of the Courtlaud Institute and Surveyor of the King's Pictures. I wrote it here.
I quoted from here [Oleg Tsarev/Nigel West book description] more details: «Triplex has been considered too secret a source ever to be mentioned outside the most senior levels of security and intelligence services, and none of the official histories of British Intelligence in World War II contain even a single reference to it. More sensitive than Ultra, Triplex was the codename for a joint covert operation to gain access to the diplomatic bags of neutral embassies in London and photograph their highly secretive contents. The MI5 officer selected to supervise this clandestine operation was Anthony Blunt, who also took copies for his Soviet contacts. Some of the most astonishing documents ever declassified by the KGB's archives are contained in this collection, unseen by anybody in the West since they were sent to Moscow by Kim Philby, Anthony Blunt and John Cairncross. These remarkable reports are never likely to be released by any British government, but they are of such compelling historical interest that they have been gathered together by the KGB's leading historian, Oleg Tsarev, and the British espionage specialist Nigel West, who have placed them in their proper context» [the book is indexed here].

About Triplex as a tool for intelligence in Mincemeat Operation see Ben Macintyre here.