On my Kenneth McKellar sampler the lyrics are credited to Cliff Hanley. I found this on the web and believe it refers to the well-known lyrics that McKellar sings:

"The music is traditional and old. There have been many lyrics and adaptations to this wonderful melody. Cliff Hanley was a leading Scottish writer and broadcaster. At Christmas 1951, he wrote his own lyrics to this magnificent melody at the request of Robert Wilson, who at the time was performing in a musical show at the Glasgow Empire Theatre. Cliff wrote the new lyrics and the piece was used to close the first half of the show." (http://www.silk.net/mcdermott/albums/dream/18.htm)