Director Joseph Losey found it difficult to work with Monica Vitti (Modesty Blaise), as she would invariably be accompanied onto the set by Director Michelangelo Antonioni, in whose movies she had become famous. Antonioni would often whisper suggestions to her, and she would take direction from him rather than Losey. Eventually, Losey asked Antonioni, whom he greatly admired, to keep away from the studios during filming. Antonioni complied.
Peter O'Donnell complains that of his original screenplay, only one line remains: "What do you know about Wilberforce?" However, he accepted the invitation to write a novelization of this movie. The book, based upon O'Donnell's original screenplay rather than this movie, was a huge success and spawned a series of best-selling novels until 1996. [Despite the popularity of this anecdote, one does have to point out, prosaically, that the line quoted does not, in fact, appear in the film].
Terence Stamp turned down Alfie (1966) to make this movie. His friend and former flatmate, Sir Michael Caine, made the role his own, won his first Oscar nomination, and embarked on a major international career due to its huge success.
Although Sir Dirk Bogarde (Gabriel) was very complimentary about Monica Vitti (Modesty Blaise) when this movie was being made, he also claimed, in a radio interview of twenty-five years or so later, that she was the only one of his leading ladies he had disliked, saying that she was "beastly".
The "Modesty Blaise" comic strip made two appearances of note in this movie. There is a close shot of a painting of the comic strip when Willie Garvin (Terence Stamp) is introduced, and in another shot, Modesty Blaise (Monica Vitti) is seen looking at copies of the comic strip.
