I always thought that was it Long Lankin. I'll check - -yes Long Lankin in the Penguin book of English folk songs. But thats Penguins for you - never can get anything right. It was sung to Cecil Sharp in 1909 by a nun Sister Emma from Clewer in Berkshire, but it has a spectacular history. In the Scots version, he is out for revenge - in the English version , he is merely a blood tirsty ruffian.
If there is anything I can do helpwise - don't hesitate.