"Flower of Scotland" is a good example of the Scottish mythologising of their own history (and before anyone starts - I am part Scots and yes the English, Irish and Welsh, and no doubt Americans, are just as bad) and reveals more about the views at the time of its writing than any historical event."

In what way does Flower of Scotland mythologise anything? It is simply a modern day nationalist invoking the spirit of independence as shown by the Scots at Bannockburn when they did defeat Edward's army and sent them home. It may be unnecesarily militaristic though I suspect Williamson was simply trying to write a modern day "Scots Wha Hae" type song but there is nothing mythological about it.

Saying that of course there is plenty of mythologising elsewhere in the Scottish canon.