The SNP has traditionally vied with the U.K's Labour Party for Scottish votes, so the Nationalists' success makes Labour's bid to unseat the ruling Conservative Party more difficult.
John Curtice, professor of politics at the University of Strathclyde and author of the "What Scotland Thinks" blog, predicts Labour will only hold on to between 4-12 seats in Scotland.
"A few will survive, the question is how many," Curtice told CNBC.
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He argued that the center-left Labour Party had angered some of its Scottish supporters by allying with the Conservative Party as it campaigned for a "No" vote in last September's independence referendum.
"In the past, you would get people on the Left voting for the SNP in the Scottish Parliament and Labour in Westminster elections—but that's changing," Curtice said.
And Labour are unlikely to get much of a boost from tactical voting by those Scots who would usually vote for the Conservative or Liberal Democrat parties—purely because there aren't that many of them left.