Sminky, Dominic Behan may very well be singing it on your recording, many have, but he definitely did not write the song. If Bert Jansch told you he did, then he has been sadly misinformed. Please take meselfs advice and visit the other thread linked by Ryan Martin, where you will find the real author of the song and it's meaning in the context of the play. You will also find a few other bits of information that may be of interest to you? Of course that doesn't mean that Dominic didn't add on a few verses later, but the basic song as we know it was written by Dickie Shannon...Fact!