Without looking any further... I'm guessing Kelpie is Scottish (Scottish folklore), Snakes is Northern Ireland (St. Patrick driving out the Pagans), Britannia is England (Kind of the head of the UK), and Choir/Skreem is Wales (Bad play on words).
I considered that too but Snakes are associated with Ireland (In this case, Northern Ireland not the Republic of Ireland) because of St. Patrick. And the Banshee is also Irish. So I figured Choir was Wales by process of elimination.