The Scots had an election on the constitutional question, and the Unionists won resoundingly, with far more Unionists than separatists elected. This throws into sharp relief the perpetual duty of Unionist politicians to treat separatist parties as political pariahs, not only in Scotland, but also in Wales, in Northern Ireland, and indeed in England.
Plaid Cymru (which, for some reason the BBC now just calls "Plaid", i.e., "party"!) is in a grey area, as, arguably, is the SDLP. But no one must "deal" with the SNP, nor with Sinn Fein, not because the SNP is terrorist (which it certainly isn't), nor even primarily because Sinn Fein is terrorist (although it certainly is), but because both the SNP and Sinn Fein wish to dismantle the State itself, the State being, in point of fact, the United Kingdom.
No other state exists within Great Britain or Northern Ireland, and everything therein either is itself the sovereign Crown in Parliament (within which primacy had passed to the House of Commons, elected by universal adult suffrage), or else exists by and under that sovereign authority. There can be no place for those who believe the (undisbanded) Provisional Army Council of the IRA to be the sovereign body throughout Ireland. And no more can there be any place for those who believe sovereignty in Scotland to reside with the majority of those deemed eligible to vote in a referendum outrageously held only in Scotland, who bother to vote in that referendum, and whose votes are able to be counted.