The song being played by the Santa Claus band which attacks Rose and Mickey is "God Rest Ye Merry, Gentlemen". This song is traditionally associated with the novel A Christmas Carol, written by Charles Dickens, whom the Doctor and Rose met in The Unquiet Dead. The song shares its melody with the "Venusian Lullaby" the Third Doctor sang in The Dæmons and The Curse of Peladon. The carol can be heard again in The Next Doctor.

from:
https://tardis.fandom.com/wiki/The_Christmas_Invasion_(TV_story)

Fakt, to ta melodia. Dzięki :)