In the original English version, the Swiss hotel clerk speaks English with almost no accent. In contrast, in the German dubbed version he speaks with a very heavy Swiss accent.
Mark Strong, who plays Jim Prideaux in Tinker, Tailor, Soldier, Spy in 2011, makes an uncredited cameo in the restaurant scene just before Smiley and Lacon's dialog.
When Smiley meets Saul Enderby, Enderby is wearing the "old school tie" from Eton College; repeating light blue stripes on a black background.