"The Red Flag" is a song associated with the Socialist Movement, and in the UK it is the de facto anthem of the British Labour Party and sung at the closing of their party conferences. The lyrics of the song were written in 1889 by an Irishman called Jim Connell. It is usually sung to the melody presented here which has a long history. The melody originated as a folk tune called "Lauriger Horatius" though it was later made popular by its use for the German Christmas Carol "O Tannenbaum" (written by Ernst Anshutz) whose English version is O Christmas Tree. Note that the same melody is used for a number of State Songs and College Songs in the US, so it is similar in sentiment to a patriotic song.
This piano arrangement of "The Red Flag" has been adapted by Jim Paterson based on the Anshutz arrangement of the song "O Tannenbaum". The music can be downloaded as PDF Sheet Music, or as a MIDI or MP3 file.