Fights in the Labour Party tend to break out for two reasons: conviction or necessity.

Before the election result, which entrenched Jeremy Corbyn’s hold on the party, the leadership wanted to lower the threshold to nominate candidates for the top job out of necessity and conviction.

As a point of expediency: Corbyn’s surprise win meant that no Labour MP was ever going to “lend” their nomination to a candidate they didn’t support again, which meant that for the Labour left to have a chance of making it to the full contest they had to reduce the number of necessary nominations to a level where they could mount their own leadership bids in the future. That's what's behind what Corbynsceptics have dubbed "the McDonnell amendment", which aims to reduce the threshold for a new leadership candidate from 15 to 5 per cent.

As a point of ideology: belief among the leadership that the membership is sovereign, not the parliamentary party, so the lower the threshold the better. (Chris Williamson, the Labour MP for Derby North, has called on MPs to be cut out of the process entirely.)

After the election, there is no longer an immediate need for the Labour left to lower the nominating threshold: the result has both added more Corbynites and convinced more MPs from the party’s centre that Corbynism can work. The widespread expectation is that retirements and selections in marginal seats will both mean that, whatever the result of the next election, Labour will have more MPs from the left and fewer from the centre-left than it does at present. A Corbynite successor would run into difficulties if a leadership contest occurred after March 2019 – when Labour MEPs will cease to exist due to Brexit, taking with them important left nominations – but a leadership election in the 2019 to 2022 period is not likely.

On the party of Labour’s centre-left, the opposition is, again, a combination of the two. Before the election, the dominant – not the only, but the dominant – line of thinking was that Labour party members would choose the most left-wing candidate available come what may, and that as a result, the menu of options had to be sharply limited. That’s the argument from expediency.

For Corbynsceptics, the election changed a great deal, too. (For one thing, there are now far fewer Corbynsceptics than there once were.) As most flatly concede behind the scenes, the next leadership election will feature a candidate from the party’s left regardless of what the threshold is set at.

There’s still an expedient case for fighting it, as it increases the chance of a mooted compromise floated by the trade unions that would see the threshold lowered to 10 per cent and the registered supporters scheme scrapped.

Although the registered supporters scheme has been a financial success for Labour, it is distrusted by power brokers on both the left and the right. That opens up the possibility for Corbynsceptics of one day achieving the ultimate constitutional expediency: the return to the old electoral college, which elevates the votes of MPs and affiliates at the expense of members.

As it happens, Corbynsceptics have a case against the McDonnell amendment that isn't solely about expediency, though. Conviction is that Labour’s leader must be someone who can command the loyalty and trust of the parliamentary Labour Party, although this case is rarely made publicly, at least not by senior MPs or prominent Corbynsceptics, who prefer to focus on the fact that measure is "divisive". Of course, if you can't explain why something is divisive it just looks as if you are being difficult. This speaks to the wider Corbynsceptic problem – that they look a lot shiftier than they are because they are reluctant to argue for why they want something, not merely what they want.