Well how would T'Watersons know how to pronounce it - they're from 'Ull!
My life in Folk Clubs started in Penistone, nobbut a stones throw from Holmfirth. The song was often sung at the close of an evening, and everyone stood for it, much in the way of a National Anthem. For which the rest of God's Own use Ilkley Moor. I digress - it was always sung as pratty flowers. I never knowingly heard anyone say it this way in common speech, but then when you live with something like that, you don't notice it...