I have an LP of Alasdair Gillies singing Gaelic songs. It's on Thistle Records BSLP 65, undated but I think it could be 1965 suggested by its label. He sings 'Gleann Dearg na H-Aibhne' (the red river valley) and the credits are Music trad, words by Gillies. This dates the Gaelic words and the chorus is, Thig a'nal, Thig a'nal .... as suggested by Obie as a translation of Keith of Hertford posting (December 2005. So, depending uupon the age of Keith of Hertford's friend's grandfather, I would suggest he was singing Alasdair Gillies' Gaelic words. I will try and get a complete English translation from the LP but, as the man said, it could take some time. I hope this answers the suggested Gaelic derivation of the song.