Dominic Behan again! In "The Singing Irish" (London, 1967) on page 38, where the song is printed, he says "Words & Music by Dominic Behan" and on page 124 he adds the note "In Sean O'Casey's play you will find the chorus of the song printed here, nothing more. [last two words underlined] I wrote all the verses."

This is not to say that there was not a complete song from which O'Casey got the chorus, nor does it rule out O'Casey's having written the chorus but no-one has ever, as far as I know, seen anything else like it.