Tattie Bogle - as to 'Scotch' being whisky, not people: that, I would suggest, is merely a late-Victorian genteelism, probably of temperance origin. Any of the great Scotch-Scots-Scottish writers prior to that [check out Burns, Scott, Stevenson et al] would quite uninhibitedly have indifferently used 'Scots', 'Scottish'', or 'Scotch' as their chosen adjective for the people, the language, or whatever. I would adumbrate Stevenson's description of Lord Justice Braxfield, in his essay on Raeburn's Portraits in 'Virginibus Puerisque' [Braxfield being generally regarded as the origin of RLS's 'Weir Of Hermiston'], as "the last judge on the Scotch bench to employ the pure Scotch idiom".

~Michael~