There is no legitimacy question in Thursday’s election. A government that wins a confidence vote in the House of Commons is legitimate, period. There may be questions of party loyalty, longevity and popular consent, but they are subsidiary. Britain is not a direct democracy but a parliamentary one. Voters surrender their sovereignty to MPs until the next election. Good, bad, sane or stupid, that is the rule. Nobody knows who will be able to win the confidence of a Commons majority until Friday, if then. That is all that matters – constitutionally.

Yet the legitimacy of a prospective government is being questioned on all sides since, in the case of Labour, it might depend on Scottish nationalist votes. Labour has depended in the past on Scottish MPs for a Commons majority, but this time the MPs in question are not Labour but nationalist, committed to the break-up of the union. Where then stands constitutional legitimacy?

The answer is in the same place. If the union is a union, not a confederation, it matters not a jot where within its borders that majority is obtained. Labour prime minister James Callaghan in the 1970s combed the highways and byways of Ulster for votes, as might David Cameron after Friday. Too bad if English voters did not get a chance to vote for SNP candidates. In this election they are United Kingdom voters. If Miliband chooses to survive in office in return for Scottish home rule, so be it. Gladstone’s deal with Parnell gave the same potency to the Irish.

A quite different question is that of consent. No government in modern times has enjoyed majority consent of the electorate, let alone of the British people. In the case of Scotland, it must now be clear that the present format for union is dying. A separatist lock on the London parliament may be legitimate but it will not be regarded as fair, or sensible in England. Any government that rules on that basis will suffer the undoubted anger of English, if not also Welsh and Irish, voters. Something must change.

The fate of two unions – with Scotland and with Europe – will be the towering concerns of the new parliament. Scotland can be simply disposed. The Scots appear fed up with the English, and the English with the Scots. No amount of subsidy, economic scaremongering or fake emotion can overcome this message from north of the border.

Some new format is required that must embrace parliamentary disengagement, devo-max or indie-lite or whatever. The task for Cameron or Miliband is to be architect of that format. An overwhelming SNP presence at Westminster should at least make this easier, not harder to achieve.