Thanks for your reply NazNomad, I did see that answer and, having two Morrisons stores locally, went and checked them out. No joy but staff did suggest it might be a regional line not available north of the border. (We do have some expertise in the production of life affirming beverages up here too so maybe the powers that be felt it would be unneccessary). :D
William Grant & Sons make Irish Mist. Their liqueur products were under negotiation (Sep. 2010) to be sold to Gruppo Campari, but with the rights retained for continued production by Grant's for the next 10 years. You could contact Grant's, and perhaps get a list of stockists in your area, here...