Then there is RULE BRITANNIA/MARRIED TO MERMAID

...He said that as he went down,
Great fishes he did see;
They seemed to think as he did wink,
That he was rather free.
But down he went so quickly,
Saying, ''Tis all up with me,'
When he met a lovely mermaid
At the bottom of the deep blue sea.
CHO: Singing Rule Britannia,
Britannia rule the waves
Britons never, never, never shall be slaves...

Once again I'm not suggesting this is the song in question. But perhaps a relative.