Michael Caine performed most of his own stunts. During the final ice floe scene, he almost slipped and fell into freezing water.
Ken Russell was contractually obligated to direct the film. He did not want to do it, but according to him "it was shoved down my throat".
Although the film follows the novel quite closely, for unknown reasons Karl Malden's character name was changed from "Harvey Newbegin" in the book, to "Leo Newbigen" for the film.
The 'double-diamond' logo for Midwinter's army was clearly derived from the Nazi swastika. If you think of the swastika as being two 'S's crossed in the centre, then the Midwinter logo is created by reversing one 'S' and distorting the shapes slightly to leave a small gap at the ends.
The bombers that General Stok sends to sink the convoy are actually British Canberras.
The movie contains several references to the work of director Sergei M. Eisenstein. Most notably the ice battle scene from Alexander Nevsky, the red flag (seen flying over Riga, Eisenstein's birthplace) and the wounded nurse (the frozen Kaarna) from Battleship Potemkin.
The voice of the computer heard over the phone before the titles is Donald Sutherland.
This was the third Harry Palmer film, after The Ipcress File and Funeral in Berlin. Michael Caine had originally signed a five-picture deal, but when he was reluctant to return to the role, producer Harry Saltzman let him out of the contract. Much later, though, he did make two more Harry Palmer films: Bullet to Beijing and Midnight in Saint Petersburg.