Tina Aumont was billed under her married name, Tina Marquand.
Dirk Bogarde claimed in a radio interview that Monica Vitti was the only leading lady with whom he'd found it impossible to get along.
Gabriel: [quoting a criminologist]: He said that Gabriel had the one true criminal mind. His only motive was malice.
Paul Hagen: Tell me... where did you really go that afternoon in Paris, when you said you were going to Balenciaga?
Modesty Blaise: [in a conspiratorial whisper]: Christian Dior.
Gabriel: I'm the villain of the piece, and I must condemn you to death.
Modesty Blaise: But I'm the heroine - don't I get away?
Sir Gerald Tarrant: How did you manage to get hold of a passport, Garvin?
Willie Garvin: Just through being working-class.
Sir Gerald Tarrant: You mean lower-class, surely?
Modesty Blaise: I think, Willy, that we will have to become a little more conspicuous.
Willie Garvin: I say, do you mean really flash?
Modesty Blaise: [recognising the first of two men following her]: Honolulu - the affair of the Maharajah's snuffbox... [then recognising the second, heavily tattooed man]...Dublin - murder!
Sir Gerald Tarrant: Very sinister, Minister!
Gabriel: [dictating a telegram]: A good general weeps when he sends his men into battle and the tears of the widows - widows'n'orphans - and the tears of the widows and orphans are his tears too.
Gabriel: Dear Clara Fothergill!
Gabriel: Silly dilletante!
Mrs. Fothergill: Basilio manufactures carbohydrates!
It has never been explained why the same actor, Clive Revill, plays both the flamboyant Arab sheikh and the prim Scots accountant, although it is known that he was not cast at all until just before the start of shooting.
The genesis of this film was quite complicated. The Modesty Blaise cartoon strip had been running in the London Evening Standard newspaper for several years; it was the work of Peter O'Donnell and Jim Holdaway. O'Donnell, who had devised the character, was approached to write a film script based on Modesty's adventures and Sidney Gilliatt was set to direct. It was part of the deal that O'Donnell would turn his script into a book-of-the-film novel for publication at the same time as the film's release. However, there were delays, Gilliatt dropped out, Monica Vitti replaced Julie Christie as Modesty, and Joseph Losey was - to the great surprise of everyone - signed as director. Losey ordered many changes to the script, O'Donnell left the project in high dudgeon, his novel version appeared before the film, and many fans of the comic strip attacked the film as a travesty, although it was a box-office hit in Europe. O'Donnell wrote several more Modesty Blaise novels, which were very popular; however, the film inspired no sequels.
This film contains the only screen acting performance of Robin Fox, a famous agent (whose clients included the director of Modesty Blaise, Joseph Losey). Robin Fox, who died in 1971, was the father of James and Edward Fox, both of whom became famous in films directed by Losey; the resemblance to Edward Fox is especially striking.
Sheik Abu Tayir is seen wearing the club tie of the MCC (Marylebone Cricket Club).
The book which Sheikh Abu Tayir is seen reading in the film's final sequence, which causes him to laugh uncontrollably, is Hansard, the day-by-day record of the business of the British Houses of Parliament.