So it's a little hard to pin down a "before nationalism" period because there was always a distinct culture, identity, legal system, church etc within Scotland. I think the early half of the 18th century was the only period before WWII that didn't have some kind of rebellion or movement going on (even if many of those were limited to specific groups within Scotland such as Highlanders or Catholics). Large parts of Scotland's wealthier population also actively looked to identify themselves with the more prosperous England.

All that said, this paper (PDF warning) from the University of Bielefeld in Germany examines the idea in what seems to be considerable depth. A particular quote from William Burns in 1853 illustrates it nicely. It is responding to Viscount Palmerston, who was the Home Secretary at the time and would later go on to be Prime Minister, and who had just delivered a speech in Scotland that referred to the UK as England. Burns objected to the:

“false assumption that ‘all the people of this country’ ... are portions of ‘the people of England’, that England is the only proper political designation for these Islands