A war of words has broken out between Labour and the Liberal Democrats over Jeremy Corbyn’s appeal to Conservative MPs to make him Prime Minister on a temporary basis in order to seek an extension to the Article 50 process.

Swinson has responded by saying that the numbers don’t stack up – there aren’t any Conservative MPs who are willing to put Corbyn in office in any circumstances, and adding for good measure that there are in any case some Labour MPs who don’t want to make Corbyn PM, so it’s simply political positioning.

This is true – but the whole government of national unity conversation is political positioning anyway. There is no hope that the various Conservative rebels, former Labour MPs or Sylvia Hermon, the independent Unionist MP who has vowed never to vote in a way that could make Jeremy Corbyn Prime Minister, are going to unite around a Corbyn-led government. But there is no plausible alternative government either.

It was political positioning when it was first discussed in the Liberal Democrat leadership election, chiefly as a way of bigging up the credentials of one candidate over another (in the yellow corner, supporters of Swinson argued that that needed a candidate with strong ties to MPs in other parties, while in the ochre corner, supporters of Ed Davey argued that it needed a candidate who had been a Secretary of State). It was political positioning when Caroline Lucas talked up the possibility of a government of national unity led only by women.

It would be politically self-destructive for Corbyn to give way on the question of who heads up that government because that would involve publicly acknowledging and giving credence to the doubts that Conservative rebels and former members of his own party have about his fitness for office – it’s not serious to expect any political leader to concede that point at any time, but particularly not before an election.

But it would also be politically self-destructive for the Liberal Democrats, whose path to winning more constituencies runs through picking up disgruntled former Labour voters and a small but significant tranche of despairing Conservative voters in Tory-held seats, to concede the idea that they could ever make Jeremy Corbyn Prime Minister.

What Corbyn has done is find a way to turn the government of national unity conversation into one which isn’t simply a way for their rivals to their immediate right and their immediate left into a conversation about how Labour is congenitally incapable of working with others and mealy-mouthed on Brexit, by setting out a clear position – an extension, an election and a reiteration of Labour’s commitment to a referendum on any Brexit deal – and putting the onus on the Conservative party’s rebels to back it.

Will it fly with voters who backed Labour in 2017 and the Liberal Democrats in 2019? No idea. But it gives the party something to say at least about the national unity question.

But the reality remains that if no deal is prevented it will be via a backbench bill of one kind or another, and that a government of national unity is a idea with too many moving parts – and that isn’t really the fault of either Corbyn or Swinson.