Philip Stephens reviews how the leading British parties have used the SNP surge in their campaigns:

That said, let the nationalists remain an existential threat to the union.

You would not have grasped this from the tenor of the campaign. For Mr Cameron, the nationalists have been a stick with which to beat Labour — vote for Mr Miliband and SNP leader Nicola Sturgeon will pull the strings. The Labour riposte was that a vote for the SNP promised to put Mr Cameron back in Downing Street. The shared message has been that the party elected to rule Scotland was unfit for any role in the governance of the UK. The two leaders could scarcely have offered a better route map for the break-up of Britain.

Stephens’ complaint is a familiar one, but it raises an obvious question: how else were these parties supposed to respond to the dramatic rise in SNP support in the last few months? The committed unionist answer is that they were supposed to “put country ahead of party” as they did for the referendum last year. This amounts to saying that both Labour and the Conservatives should have reacted to the SNP surge either by welcoming it as a healthy part of U.K. political life (which they naturally don’t) or pretending that it didn’t matter to them (which they couldn’t). The real issue is that none of the unionist parties was prepared for how voters in Scotland would respond once the referendum was over. For the unionist parties’ leaders, it seems that they thought the ‘No’ vote meant that they could go back to ignoring Scotland, but most Scottish voters had other ideas. Cameron thought and claimed that the ‘No’ vote had “settled” things, but the decision to vote on the question of independence had so completely unsettled–and enlivened–politics in Scotland that things could not go back to the way they had been before.

If some calculated campaign rhetoric is enough to pave the way for the break-up of the union, then the union is probably not long for this world in any case. Any political union so fragile that it risks being wrecked by normal electoral competition is one that isn’t going to survive for very long no matter what its leaders do. That campaign rhetoric points to the political estrangement between the different parts of the U.K. that unionists wish would go away, but which has been growing for years before the current campaign. Stephens’ column title refers to “broken parties that may break Britain,” but it might be more accurate to say that the leading parties are in such bad shape in part because the U.K. has been on its way towards dissolution for some time. This election may just be the occasion when that becomes impossible to ignore.