Quoting from Elisabeth Poston's The Penguin Book of Christmas Carols, The Holly and the Ivy is one of the finest English folk carols. The words and tune were collected by Cecil Sharp. The holy and ivy refer to ancient male/female fertility rites and the merry organ refers to the portative organ used in medieval times. This version is very similar to the version sung by Tyneside Maritime Chorus who have it in their Christmas repertoire.
This song may be found in the Tyneside Maritime Chorus songbook

Lyrics