Sorry, Masato, but that's the Trelawny song I already know; Cornwall For Ever, with a completely different tune, ends each verse, however, with "Cornwall for ever and shall Trelawny die, then twenty thousand Cornishmen will know the reason why."

Let me try the link again. This should take you to a page of Cornish Folk Songs with Cornwall Forever at the bottom (scroll down and click). Perhaps someone with better audio reception than me can get all the words. It's tantalizing just to get the familiar bit.