The date in which the most sophisticated and deadly spy network in the world advised the President of the United States to step outside all legal channels to preserve the security of the country was 15th October 1972. The date in which they thought they may have made an incredible mistake was 15th September 1973.
This film's opening prologue states: "That which enables a wise ruler and a good general to strike, to conquer and to attain goals beyond the reach of ordinary mortals is "Prior Knowledge" SUN TSU (5th Century B.C.). Some versions of this movie feature the following title card addenda to this movie's prologue: "In the modern world, this 'prior knowledge' is synonymous with 'Secret Services'. Novelists call it...'Espionage'."
In addition to the parallels between MI6's Philip Boyle in the film and Kim Philby in real life, there is another parallel between the head of the CIA characters. The name of the Director of the CIA in the film, Allan Davies, seems to be a tribute to Allen Dulles, who in real life was the Director of the CIA from 1953 to 1961. Beside their names, the resemblance of facial lines of these two men is remarkable as well.