peejaycee
I've come late to this discussion but would like to add my pennyworth to the debate. With an English Army and (and their regimental musicians) based in Ireland for centuries their must have been considerable interchange of music. I have always believed this to be an Irish air. The reason we are a little protective of our songs is that the people who wrote them were the last of the bards who, (intentionally or not) kept this aspect of our culture alive in the teeth of serious attempts to eradicate it. Ironically, much of what is preserved was preserved by English scholars. As regards to the lyrics (from the John McCormack recording) I think :-

Her eyes have the glance of the sunlight as it touches the deep sea wave,
And more than the deep sea trasure, the love of her heart I crave.