Some papers, including the Express, have reported about the folk roots of some carols.

http://www.express.co.uk/posts/view/146061/Hymn-expert-reveals-a-Christmas-carol-s-folk-roots

Actually the tune used for "On Ilka' Moor" was a hymn tune originally!

In 1805 a hymn tune called Cranbrook was composed by a cobbler of Canterbury, Thomas Clark. A hundred years later it was still being sung in Wesleyan Chapels at Christmas time to 'While Shepherds watched their flocks by night'. It was originally composed as a setting for While Shepherds Watched. Only later did it become more familiar for On Ilkley Moor Without a Hat.

According to tradition, the members of a Halifax Wesleyan Church were picnicking beneath the Cow and Calf rocks near Ilkley, after their annual walk across the moors from Dick Hudson’s, when two of their party disappeared into the bracken. On their return to the main group, a member of the choir bellowed out “Wheer wor ta bahn when ah saw thee?” “Tha’s bin a-courtin’ Mary Jane”, commented another. Further lines in common metre were contributed until the choir burst naturally into the tune Cranbrook.

Over the years, more verses have been added, and it has been accepted as Yorkshire’s “National Anthem” It is still used by some church groups in the Halifax area for 'While Shepherds'!

The Yorkshire Dictionary (Arnold Kellett, 2002) stated that the song (i.e., the lyrics) probably originates from the Halifax area, based on the dialect used in the song, which is not common in all areas of Yorkshire.

The title is seen in various transcriptions of Yorkshire dialect, but is most commonly On Ilkla Mooar [or Moor] baht 'at, i.e. "On Ilkley Moor without [wearing] a hat". The song's origins are believed to be as a ditty to poke fun at a courting couple, as sung by a mischievous local choir.