I would love to add something extra or original regarding this most powerful ballad but most of it has been said. I managed to make a recording of MacColl singing it at Newcastle's Barleycorn club back in 1970 (now long gone - both the club and the recording)and his version is the one I like the best. I have heard several variants since then, some where Gregory manages to save both Annie and the child and others where all three end up drowned. MacColl's hits the right ballance of pathos, sadness and passion.
It also mentions South Shields football team ("Oh row your boat ye Mariners"!)