I was shocked to discover that it is more than three years since John Barleycorn featured as a Sunday music video.
Last time the song appeared - in December 2008 - I chose a live performance by Traffic from their great 1972 Santa Monica gig. This is a recent Steve Winwood solo performance and it suggests that his voice has improved with the years.
I see that the late Helen Elsom left a comment on that 2008 post suggesting that John Barleycorn is not a true folk song but, at least in part, the work of a modern antiquarian. The Wikipedia entry on the song shows that some have shared her doubts:
in their notes to the Penguin Book of English Folk Songs (London, 1959), editors A L Lloyd and Ralph Vaughan Williams ponder whether the ballad is "an unusually coherent folklore survival" or "the creation of an antiquarian revivalist, which has passed into popular currency and become 'folklorized'".But it says that Lloyd and Vaughan Williams also note that it is an old song, with printed versions dating as far back as the 16th century.