Source author John le Carré included 'The Spy Who Came in from the Cold' as one of his four best novels during an interview on 5 October 2008 on BBC Four. The other best works he selected were 'The Tailor of Panama', 'The Constant Gardener' and 'Tinker, Tailor, Soldier, Spy'.
When Richard Burton became a superstar, he insisted on casting his friends from his days at the Old Vic and West End (London's equivalent of Broadway). That is why Claire Bloom, who is clearly too old to be a teenager, was cast as Nan Perry. Other friends of Burton's cast in the film included the great stage actor Sir Michael Hordern and Robert Hardy.
Author John le Carré worked for British Intelligence MI5 and MI6 during the 1950s and 1960s and worked in Berlin where this film is partially set. Le Carré was there when the Berlin Wall was being constructed. Le Carré drew on this real life experience when he wrote the novel of 'The Spy Who Came in from the Cold'. The novel is set about a year after the Berlin Wall was built.
Richard Burton and co-star Warren Mitchell were Royal Air Force cadets together at Oxford in 1944, where they knew one another and became friends. From 1944-47, when both were demobilized, they were stationed together at times in Canada and back in England.
The character of George Smiley, John le Carré's famous character, was renamed Charles Dobbs for John le Carré's The Deadly Affair (1966) because this film's Paramount Studio had bought the rights to the Smiley name when they produced this film.
The character of Hans-Dieter Mundt (played by Peter van Eyck in this film) was changed to Karel Harek aka Blondie for John le Carré's The Deadly Affair (1966) because this film's Paramount Studio held the rights to that character's name from this film.
The name of the character of Liz Gold from 'The Spy Who Came in from the Cold' novel was changed to Nan Perry (played by Claire Bloom) for this film. It is considered that the reason for this was because lead actor Richard Burton was married to actress Elizabeth Taylor at the time, and changing the character's name prevented any possible name-jibes that could be vented from the media.
This film's title was spoofed in Dr. Goldfoot and the Girl Bombs (1966) which translates literally into English as "The Spies who came in from the Frozen Custard", or more commonly, "The Spies who came in from the Semi-Cold". The word 'semifreddo' in the Italian language version's title is a jokey reference to the name of an Italian ice cream dessert called semifreddo which literally translates into English as 'semi-cold'.
First of two screen adaptations of a John le Carré story scripted by Paul Dehn. The second would be The Deadly Affair (1966) released in the next year. Just before this movie, Dehn also co-wrote the script for the James Bond movie Goldfinger (1964).
Writer John le Carré partially based his famous George Smiley character on a friend, the Lincoln College tutor and Oxford University don, the Reverend Vivian Green. Smiley was also based on le Carré's boss at MI5, Lord Clanmorris, who wrote crime novels under the pseudonym of John Bingham.