Kingsfold, which is Vaughan Williams' arrangement of this tune (not Holst's as someone above seemed to be saying) is used as a tune for at least 53 hymns, the two most popular being "O sing a song of Bethlehem" and "I heard the voice of Jesus say". Its use as a hymn tune goes back to 1906, so probably predates "Star of the County Down" (but definitely not Gilderoy, and probably not Maria Marten). Vaughan Williams got it from Broadwood and Maitland, as others have said, but knowing his conventions he would probably have done so after first hearing it sung in a pub in the village of Kingsfold, Sussex. His "Five Variants..." were composed much later.

http://www.hymnary.org/tune/kingsfold_english