God Rest Ye Merry, Gentlemen

From Tardis Wiki, the free Doctor Who reference

"God Rest Ye Merry, Gentlemen" was an ancient Earth Christmas carol. It was this song that was being played by a group of robotic Santas before they attacked Rose Tyler and Mickey Smith on Earth. (TV: The Christmas Invasion) The Santas also played it just before abducting Donna Noble in a taxi. (TV: The Runaway Bride)

A group of children were singing this song when the Tenth Doctor arrived in London on Christmas Eve 1851, just before his encounter with the Cybermen. (TV: The Next Doctor)

The song was also playing before Wilfred Mott entered a church commemorating "the Sainted Physician" where he first met the woman. It was also played by a brass band shortly before the Tenth Doctor regenerated. (TV: The End of Time)

The melody of the carol was the same as that of the "Venusian lullaby" occasionally used by the Third Doctor to lull his foes into a state of tranquility. (TV: The Dæmons, The Curse of Peladon, PROSE: Venusian Lullaby)

Professor Capra sang a version of "God Rest Ye Merry, Gentlemen" to himself. (AUDIO: Flip-Flop)

God Rest Ye Merry, Gentlemen