The Robert Tannahill connection is interesting.
We have the song "Wild Mountain Thyme" or "Will ye go, Lassie, go?" that was folk processed down from Tannahill's "Braes of Balquidder", passed over to Northern Ireland and was collected from the McPeake family. This became endemic in folk clubs - certainly in Australia - as the "Go home everyone and let me clean up" song that ended the night.
Australia's unofficial anthem - certainly our best known song - Waltzing Matilda has a tune that descended by various arrangements, (mis)rememberings and fittings to 'Banjo' Paterson's words from the tune set to Tannahill's "Bonny Wood of Craigielea".
I also seem to remember reading that the Irish rebel song/unofficial anthem, "Wearing of the Green", is from an 1848 musical play (about the 1798 rebellion) by Dion de Boucault (??? dubious about spelling) and uses a Scots tune that he filched from another setting of a Tannahill poem.
Maybe we should go digging for a Tannahill level in the archeology of a few more national icons.