Jon reveals “I first heard this from The Copper family, and it’s probably the song I come back to most when trying to think of a good chorus song to sing.”
This one apparently dates from 1836 and the words of Charles Jeffreys set to music by Samuel Nelson. You can link to the sheet music here. My understanding is that the tune has been changed as a result of a misinterpretation of the Copper’s version, although they may well take credit for rearranging it. Jon originally got it from the Coppers, but admits his version may have wandered from theirs. You can see more about the song at this Mudcat thread that also suggests a couple of similar forebears. Allendale is in Northumberland, although the first verse has Mary leaving her “Highland cot,” which suggests she crossed the border. It’s possibly, however, Allendale is simply a name that fits the song and the use of Highlands may be a reference to Scotland in general rather than the specific region. Mainly Norfolk carries the details of the Coppers and Nic Jones versions, but whichever way you look at it, this is lovely and the chorus was unexpected. This was apparently recorded on the Bellowhead tour bus (which probably explains the slightly odd acoustic) with the help of Paul Sartin and Sam Sweeney and that chorus sure works a treat.