No Murray on Saltspring, we're not getting mixed up. There are (at least) two songs about blokes marrying mermaids, and both of them can be and are sung with choruses incorporating Rule Brittania.

That's the beauty of the folk process. Choruses, verses plots and tunes can move around as they wish, as we wish.

There is no "right" or "wrong" way. There are original versions, which can sometimes be traced. There are versions which sing well, and some which don't sing so well. There are cases where one song will divide into two, and others where two songs will converge into one.

"There are four and twenty ways
of constructing tribal lays
and every single one of them is Right.
(Rudyard Kipliong.