Say this for Ed Miliband: he never misses a chance to plumb fresh depths. The Labour leader epitomises the banality of mediocrity. Each time you think he might have something useful to say, he deflates your expectation by revealing he has nothing to say at all. Yesterday, Mr Miliband ruled out a coalition with the Scottish National Party.

There will, he said, be no SNP ministers in any cabinet led by Edward Samuel Miliband. No sir, there will not. Alex Salmond, if, as seems likely, elected to represent the Gordon constituency, will not be Deputy Prime Minister in a Labour-SNP coalition.

The impressiveness of this declaration of intent was only marginally undermined by the fact that no-one, least of all the SNP, wanted a formal coalition between the parties in the first place. Mr Miliband might just as sensibly have ruled out a coalition with the Monster Raving Loony party. Like any putative coalition deal with the Nationalists, that was never on the table either. So Miliband’s statement amounted to nothing so much as admitting that no amount of wishful thinking can transform a losing lottery ticket into a winning one.

Besides, as Nicola Sturgeon observed, “This was a lot of hype to rule out something no-one was proposing.” Miliband’s statement “is absolutely fine from our point of view.” That welcome should, on its own, be enough to chill Labour blood. If the SNP are happy, recent political history suggests Unionists have reason to be worried.

Indeed, it is becoming ever clearer that the Nationalists have trussed Labour up like a chicken ready for roasting. All that remains to be decided is whether Labour will be cooked low and slow or fast and high. The outcome is not in doubt; merely the means by which it will be delivered. The result is the same: the chicken is roasted.

The truth is that a weak Labour government dependent upon SNP support on an issue-by-issue basis suits the Nationalists almost as well as another term in office for David Cameron. The SNP have no desire to become entangled in the thickets of any formal coalition apparatus. Better by far to remain on the backbenches exerting influence as and when they see fit. This will doubtless be presented as a means by which Labour can be “kept honest” but it really offers the SNP the gift of power without responsibility. They will claim credit for what they want and absolve themselves of responsibility for anything that seems disagreeable.

In that respect, a large SNP contingent at Westminster will enjoy the same kind of teflon-status the party has hitherto enjoyed while exercising power at the Scottish parliament in Edinburgh. Labour take comfort in the thought the SNP would never dare vote down a Labour government and, potentially, hand the Tories another shot at power but the truth is there’d be no need for the SNP to act in such a reckless or provocative fashion.

Why, in any case, would they do so when a weak Labour government serves their interests so effectively? Moreover, the requirements of fixed-term parliaments make a subsequent, snap, election much less probable. The SNP could keep Labour on a leash without risking a fresh Tory government. If that provoked some kind of English “backlash” then so much the better.

Not that a Conservative victory in May would depress the SNP either. Many of the party’s grass-root activists might deplore such an outcome but the leadership is keenly aware that another term in office for David Cameron serves the Nationalists well. Even if the Tories were to somehow treble their Scottish representation the party will remain a minority enthusiasm in Scotland. The SNP would be sure to condemn this lack of “democratic legitimacy”. Once again, they would argue, Scotland will be forced to live with a government for which it did not vote.

It requires no great measure of imagination to see how this could be used to the Nationalist’s advantage. Meanwhile, the converse is also likely to be true: an SNP landslide in Scotland would deprive even a minority Labour government of its “legitimacy” in Scotland too. In either scenario, if the SNP win 40 or more Scottish seats the nationalists will be able to claim that only the SNP really represents the Scottish people. Scotland will have chosen, but England (and Wales) will have decided.

If the election is viewed as being one for the whole United Kingdom, this remains reasonable. Increasingly, however, it is not viewed in such terms. There is the Scottish election, there is the Welsh election and there is the English election. It seems unlikely any putative government will enjoy a convincing mandate in all parts of the kingdom.

In any case, Labour’s own chickens are coming home to roost. The so-called “people’s party” spent years demonising the Conservatives in Scotland, presenting them as a hostile and alien force. They were, to use an ugly but increasingly popular term, “othered” and rendered quite beyond the pale. Now the Nationalists are deploying the same arguments, the same rhetoric, against the Labour party. It turns out that Labour are just as vulnerable to this assault as the Tories were. That explains why, like the Tories before him, Jim Murphy feels the need to stress Labour’s “patriotic” credentials.

Miliband’s decision to rule out an impossible, unwanted, coalition reveals Labour’s weakness in England, too. English voters dislike the idea of a government beholden to a party that aims, in the medium to long term, to break up Britain. It is becoming clear that Labour cannot rely on its Scottish vote to make up for a poor performance in England. It must win in England too or it will be sunk. If that means cutting Scotland off — and leaving Jim Murphy to salvage whatever he can — then so be it.

The problem for Miliband, however, is that his “offer” to voters — no matter where they live — is so pitiful. If it were twice as impressive it might still be reckoned lacklustre. Indeed, Labour’s campaign is quite spectacularly banal. At the weekend Mr Miliband unveiled Labour’s latest “pledge card” listing the party’s bold promises to the electorate. Labour favours “a strong economic foundation”, “higher living standards”, an “NHS with the time to care”, “controls on immigration” and, most daringly of all, “a country where the next generation can do better than the last”. No-one can disagree with any of this. It is candy floss disguised as cast-iron. Coming soon: Labour come out for sunshine.

This election is less a contest between potential Prime Ministers and more a race to see which mainstream leader loses less badly. No wonder it is a less than edifying sight. No wonder, too, that the SNP — united, strongly-led, and with a purpose — seem destined to thrive regardless of how the votes are cast in the other parts of the United Kingdom. Heads they win; tails they win too.

A version of this article appeared in the Scottish Daily Mail on March 17th, 2015.