SNP want to prove they can be trusted, then at the next election they go for a referendum mandate. Break up the UK? Nope, they need the referendum to do that and they won't stand a chance if they don't behave at Westminster. They are getting a bit of a vote to punish labour, don't think for a second that vote won't swing back if the SNP fixate on a referendum or start playing silly buggers down south.
SNP are trusted at Holyrood, they need to prove they can be at Westminster too.
I voted YES in the referendum, we lost - that means we need to be part of the UK and I won't vote for SNP again after this election if they cannot act like exemplary politicians at westminster