I listened to Today the other day and was surprised to hear during the 8 am News Bulletin that it has been claimed that the Christmas carol 'While Shepherds Watched their Flocks by Night' was originally sung to the tune of the folk song 'On Ilkla Moor Baht 'at'.
I understand, from 'The New Oxford Book of Carols' (Ed. H Keyte & A Parrott) that the tune is known as 'Cranbrook' and was written by a shoemaker from Canterbury called Thomas Clark. It was first published in Clark's 'A Set of Psalm & Hymn Tunes' in 1805. Although Clark wrote it for a different hymn it became associated with 'While Shepherds Watched their Flocks by Night' which was possibly written by Nahum Tate in around 1700. According to Wallace Harvey in his book 'Thomas Clark of Canterbury' "the words of 'On Ilkla Moor Baht 'at' were composed by the conductor of the Heptonstall Glee Choir" in around 1877 to Thomas Clark's tune. The song increased the tune's popularity and the words and tune combined have entered the folk tradition.
I have not found any suggestion that the tune was known prior to Thomas Clark's publication of it. Therefore it seems that this is a hymn tune which has become a folk song rather than the other way round as claimed, unless new evidence has come to light. I also suspect the BBC reporter of turning the story round to make it more 'interesting'. I emailed the Beeb about all this but not surprisingly had no reply. I think it is just as interesting that the 'pop' songs of the day should become folk songs which I suspect is a process that is going on today. Maybe in two hundred years time Beatles tunes may be thought of in the same way as Cranbrook is now?