Sir Dirk Bogarde was cast at last minute. Bogarde originally turned down this movie and Sir Tom Courtenay was cast, then Bogarde changed his mind due to financial reasons - he had taken considerably less than his usual salary for O Criado (1963) in order to get the film made. As he was in his early 40s at the time, he was rather too old for the role of "Nicholas Whistler," who is clearly supposed to be only in his twenties. Five years later, Courtenay ended up starring in another spy comedy, "Otley, Herói Sem Vocação (1969)."
One of five spy movies that Director Ralph Thomas made in just over a decade, the others being "Os 39 Degraus (1959)" and three consecutive back-to-back-to-back spy movies made during the late 1960s, "Bonecas que Matam (1967)," "Atentado ao Alto Comissário (1968)," and "algumas garotas fazem... (1969)."
Shooting took place in Padua, Italy representing Prague, Czechoslovakia. Pinewood Studios was where most of the interiors were shot. The cast and crew also traveled to Padua, Italy for some location shooting since the filmmakers were not allowed to shoot in communist-controlled Czechoslovakia.
The code number of Nicholas Whistler (Sir Dirk Bogarde) was 008. This movie's American titles "Agent 8¾" and "Agent 008¾" vary this. These titles spoof James Bond's code number of 007. This movie's storyline actually has an Agent 007 who is killed off at the start of the movie.
The movie was released as Agente Secreto Desafia Moscou (1964) when it premiered in England in March 1964, but it was then re-titled "Agent 8¾" for its release in the U.S., where it also had the similar promotional title of "Agent 008¾."