Good King Wenceslas

"Good King Wenceslas" was a Christmas carol.

While treading carefully through the minefields of Skaro, Sarah Jane Smith mentioned Good King Wenceslas to the Fourth Doctor and Harry Sullivan. (TV: Genesis of the Daleks)

Mr Copper incorrectly described Good King Wenceslas as the ruler of the UK. (TV: Voyage of the Damned)

Behind the scenes
The lyric "The Feast of Stephen" (with the spelling of the name changed to Steven for Steven Taylor) was used as the title of the infamous Christmas-cutaway episode of The Daleks' Master Plan.