I think you mean the English have always sneered at the Scots, since English, Scots, Welsh, and Ulstermen are all British. Saying that the "British" are prejudiced against the Scots is like saying the Americans are prejudiced against people from Colorado.
And btw, Scotland is not a monoethnic country. The Lowland Scots are of Anglo-Saxon and Brythonic descent rather than actual Gaelic Scots, and non-Gaelic Scots are quite capable of being as anti-Irish as any Englishman.
I'm sorry if I seem to be overstressing a minor point but as a redneck of English rather than Scots-Irish extraction the identification of "British" with "English" (and the assumption that Welsh, Scots, and Ulstermen are not British) drives me absolutely bonkers.
And it is England, not Scotland, that has paid the highest price for the Union. Scotland retains its unique identity; England is merely "Britain."
Whoops. I was thinking England but those fingers were faster than the brain... then there’s always the first draft follies. You are correct.