Hi Helen - I'm 100% certain that the tune Stivell, and certainly the harp player in the link provided by "Iains" is the same tune as the "Tannahill Weavers" recorded as "Galley of Lorne". The difference is that both Stivell and the harp player have changed the rhythm, but take it from me, it is the same tune. I'd say that the "Tannahills"' version might be closer to the original.
I just heard from my brother that fiddler John Martin is going to be leaving the "Tannahills", and is doing his last gig with them near Dundee next Saturday. I'm very tempted to go to that, and if I do, I'll ask Roy and Phil - the 2 original members who played on the first album where they got the tune from, and what they know about it.