Janan Ganesh sees English impatience with Scotland as a bigger threat to the U.K. than the SNP:

Unionists pretend otherwise but their cause is itself a kind of nationalism: its premise is that the British are a people. And while most unionists are temperate, some show a hectoring impatience with those on the English right who are not willing to submit their interests and ideology to the transcendent cause of the UK, forever. They say Mr Cameron puts the union in peril by seeking English votes for English laws in Parliament, and invoking the SNP as a wedge issue to save his electoral hide. But the prime minister did not confect a problem out of nothing. The problem exists. There are constitutional inequities in the union born of devolution. Many warned of these at the time. They were shouted down for their trouble.

And if the UK can be mortally wounded by a five-week campaign run by a hopelessly unpopular party, is it so robust anyway? What should trouble unionists most about Tory efforts to mobilise the English is that the effort required is so minimal. “Voters start ranting about the SNP unprompted,” testifies one startled Conservative. The grievances are inchoate — a hunch that people “up there” are taking liberties with “our” tax revenues. But they are more likely to harden than to go away. Unionism must take an interest in England before England loses interest in unionism.

One problem for the unionists is that they have been making two very different kinds of arguments in Scotland and England, and the one undermines the other. The unionists in the referendum campaign emphasized that independence would be too costly and would leave Scotland worse off than it was. Unionist critics of the ‘No’ campaign complained that it was an uninspired, bloodless case for the union, but it was good enough at the time to persuade most Scottish voters that independence was too big of a risk to take. Meanwhile, the unionist message to English voters is that they should be expected to subordinate their interests to the preservation of the union no matter what. They appeal to an emotional attachment to the union that does not appear to exist for a lot of people in England. The union was pitched to Scottish voters last year as being in their best interest, but it is presented to English voters as something that they must maintain as a matter of duty. No wonder so many English voters are unhappy with the prospect of possibly having the make-up of the next government decided by the election results in Scotland.

In their own way, many unionists have been making the same mistake with English voters that Labour politicians made in Scotland for years, which is to assume that their support will always be forthcoming and that nothing ever needs to be done to earn it. Labour took Scottish voters for granted for decades, and very soon there will be almost no Labour MPs from Scotland because they neglected the interests and concerns of these constituents for so long. If unionists keep taking English support for the union for granted, and if they keep presenting it as something that the English must support to their own disadvantage, it may not be that long before they find that most English voters will be happy to be rid of it.