Most modern recordings and performances of the Mikado's solo, "A More Humane Mikado" feature a bloodthirsty laugh between the verses. This touch was added by Darrell Fancourt, a D'Oyly Carte performer from 1920-1953, and has been copied ever since - which is why the laugh is not performed by Richard Temple (Timothy Spall).
When Richard Temple performs "A More Humane Mikado" during the dress rehearsal, the script cuts out the third verse. Partly this may have been because of time considerations, but also because the original verse used the word "nigger" and was not changed until the 1940s.
In his dressing room after the performance of "Princess Ida" in which he strains his voice, Richard Temple recites some dialog from "H.M.S. Pinafore". Temple created the character of Dick Deadeye in "H.M.S. Pinafore", and sang it during the initial 1878 run and several subsequent revivals.
Similarly, in the scene where Leonora Braham and Jessie Bond sing a short excerpt in their dressing room (ending in "he was a little boy") during an interlude of "The Sorceror", the song is from the Gilbert & Sullivan opera "Patience" ("Long years ago..."), sung by the characters Patience and Angela, which Leonora Braham and Jessie Bond had performed in the initial 1880 Opera Comique production.
As Sir Arthur Sullivan and his mistress Fanny Ronalds casually discuss aborting their baby, the incidental music is a passage from Gilbert and Sullivan's "Iolanthe." The lyric which goes with the music is, "Plead for my boy. He dies."
In the actual opening-night performance of "The Mikado", the Act 2 finale began with "The Threatened Cloud Has Passed Away". This version was felt to be too short, so "For He's Gone and Married Yum-Yum" was later added, as seen in the film and modern performances.
Mike Leigh was so frustrated with the continued relegation of his movies to art house cinemas instead of wide release that he joked that he would have cast Arnold Schwarzenegger as both Gilbert and Sullivan if his budget had permitted it.
Though the film shows Gilbert coming up with the idea for The Mikado after visiting the Japanese exhibition, in reality he had already finished writing the first act of the libretto by the time the exhibition came to London.
At lunch, George Grossmith, Durward Lely, and Rutland Barrington discuss the news of the defeat and death of British General Charles Gordon in Khartoum. The British relief force which failed to rescue Gordon was commanded by General Sir Garnet Wolseley. Wolseley was one of Victorian England's most flamboyant and well-known military figures, and widely believed to have been the "model of a modern major general" upon whom Grossmith based his portrayal of Major General Stanley in "The Pirates of Penzance."
Much of the six-month-long rehearsal process consisted of the cast discussing and doing detailed research on Victorian social and personal habits, speaking patterns, news events, and the mechanics of theatrical production during that era.
There are three Shakespearean quotes. The first is a line from Macbeth Act III, Scene 3 "O horror, horror, horror!...", spoken by Gilbert at breakfast in relation to the prospects for an extended run for 'Princess Ida'. The second is from Othello, Act I, Scene 1 : "What a full fortune does the thick-lips owe,/ If he can carry 't thus!" , spoken at the restaurant when discussing General Gordon's death at Khartoum. The third is also from Macbeth, Act II, Scene 2 : "A little water clears us of this deed," spoken by Helen Lenoir when comforting Rutland Barrington, who was ill from eating oysters.
At the beginning of the scene showing the recital in which Sullivan's song "The Lost Chord" was sung, the pianist is shown playing the last few bars of the Nocturne No. 4 in E-flat major, Op. 36, by Gabriel Fauré. The piece was first published in 1884, not long before the events depicted in the film.
Not only did all the actors do their own singing, but everyone in the cast, including the pit orchestra and the actors who play instruments in the film, actually played the music they are seen to play.