What would happen in the Rutherglen by-election if the YouGov poll is exactly right?

Last week's YouGov poll was the first relatively good poll for the SNP for several months .

But it was accompanied by a flat statement from John Curtice that the swing back to the SNP wouldn't be enough for them to hold the Rutherglen & Hamilton West constituency in the forthcoming by-election.

In practice I would expect Labour to win by more than five points in practice.