God Rest Ye Merry, Gentlemen
From Tardis Wiki, the free Doctor Who reference
God Rest Ye Merry, Gentlemen was a Christmas carol]]. A group of children were singing this song when the Doctor arrived in London on Christmas Eve 1851, just before his encounter with the Cybus Cybermen. (DW: The Next Doctor)
Behind the Scenes
By coincidence or by design, the melody of the carol is the same as that of the "Venusian lullaby" occasionally used by the Doctor to lull his foes into a state of tranqulity. (DW: The Daemons, The Curse of Peladon and MA: Venusian Lullaby.)
The Next Doctor broke the pattern of Doctor Who Christmas specials featuring original songs by Murray Gold; in fact, it is the only song heard in the special.