Thanks to all for those contributions. Glad that I wasn’t imagining James Watt, and if I had had the wit to look into The Green Linnet I would have found out the date of 1817 for myself. Probably that was where Watts got into my head. So, Fraser seems to have published the poem twice, on a broadside and in a chapbook (if Peter Wood is correct about the broadside and didn’t mean the chapbook). The chapbook doesn’t name a tune, and the date on the broadside referenced by Martin, which names both Watt and The Braes of Balquidder, is, sadly, illegible, although I suppose from the preface that it was printed nearly forty years later, during the Crimean War. The Braes of Balquidder was composed by 1810 (the year of Tannahill’s death) but it seems that it wasn’t published until the period between 1821 and 1824 (though of course, it was possibly current much earlier). But presumably The Isle of St Helena became a song in the early 1820s.

A couple of minor pedantic points - The Poet’s Box in Glasgow doesn’t have any direct connection to The Isle of St Helena as it started up in 1849. And Wood says that the song was published in Ireland, though only a couple of times.

The original poem had only five verses. I wonder who introduced the Prince of Gehenna into the song, or wrote the verse with the marvellously bitter line “on a prisoner of war you may now hurl defiance”. I would guess an Irish author.

For any future readers of this thread who do not have access to Peter Wood’s The Green Linnet, he also tells us that the lovely melody with which we are all familiar nowadays is not The Braes of Balquidder (which was the ancestor of the Wild Mountain Thyme tune). Wood says that “this tune was sent to Frank Kidson in 1892, as ‘sung by an old soldier in the streets of Dublin’. So, there is an Irish element to the song after all.” Our thanks to that old unknown soldier, and the lover of folk song who took the trouble to pass it on to Kidson.

Tracing the history of songs is an irrational hobby of mine so I am indeed grateful for this help.