I'm just reading Master and Commander by Patrick O'Brian, and he has a couple of the characters - Stephen Maturin and James Dillon, United Irishmen working on the ship - singing a song about the Wild Geese that I've never heard. Here's the verse he quotes, and a couple of surrounding lines:

"When I was last at home," said James, filling Stephen's glass, "we waked old Terence Healy. He had been my grandfather's tenant. And there was a song they sang there has been in the middle part of my mind all day - I cannot quite bring it to the front, to sing it."

"Was it an Irish song or an English?"

"There were English words as well. One line went

Oh the wild geese a-flying a-flying a-flying
The wild geese a-swimming upon the grey sea."

Stephen whistled a bar and then, in his disagreeable crake, he sang

"They will never return, for the white horse has scunnered
Has scunnered has scunnered
The white horse has scunnered upon the green lea."

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Does anyone know this song? I don't think I've ever heard it, yet it's oddly familiar.