I always heard the title character referred to as False Longshanks in the version of the song I grew up with. When I grew old enough to research such things, I interpreted Longshanks to be a fairy or demon lover of the nurse's or possibly the lady's (the malevolent fairies are often known as blood drinkers in Celtic legend.) A possible suggestion of fairy origins lies in the connection of certain birds with the supernatural. The last two stanza went, as best I remember:

"Oh harsh cries the hoodie who roosts in the brake,
But louder cried Longshanks when they bound him to the stake.
And wild screams the hern from the fenland so wet,
But wilder screamed Longshanks as the faggots were lit.
Then sweetly sang the wren as she soared up on high,
"Thou art a villain, False Longshanks, and deserve well to die." "