In my diary, I have the words “Labour leadership election?” pencilled in for 23 September. The only thing I got right was the question mark. The words were written when Theresa May called the snap election; along with many politicians in all parties, I believed she would win a big majority. And that Chuka Umunna and Yvette Cooper would then challenge Jeremy Corbyn for his job.

Instead, we might have a Conservative Party leadership election this autumn. At a time of political turmoil, one thing is certain: Corbyn is totally secure. After his brilliant election campaign, many of his Labour MP critics admit they were wrong about him, and that he has earned the right to lead the party into another election.

Despite that, the Corbynistas have been less magnanimous in their internal victory than their opponents have been in defeat. In remarks which deserved more attention, Ian Lavery, an ally promoted by Corbyn to Labour chair after jointly running the party’s campaign, said Labour might be “too broad a church”. It was seen as a declaration of war by Corbyn’s critics: if they could not accept that the party is now a socialist one, they should get out.

It might have been dismissed as an isolated incident. But it is not. Corbynistas are moving quickly to cement their grip on the party. Despite a superficial post-election unity, some MPs previously critical of Corbyn have already been put on notice that they will be deselected unless they toe the left-wing line. There are plans to change Labour’s rules – to bolster Corbyn’s position on the party’s national executive committee (NEC); ensure that a left-winger would be on the ballot paper in future leadership elections and possibly make it easier for constituency parties to deselect MPs. An unnecessary battle over the rulebook will loom large at the party’s Brighton conference in September.

The 20 new appointments to Labour's front bench

When Corbyn reshuffled his frontbench pack, only one critic – Owen Smith – was brought back into the Shadow Cabinet, leaving talented figures languishing on the backbenches. Corbyn allies insist several critics were handed junior frontbench roles, saying it would be wrong to change a loyal, winning team.

Corbyn's honeymoon with the voters continues – and he is a more assured Commons performer than before the election – but among his old enemies, it is over. The left-wing manoeuvring has alarmed those on the party’s centre-right (although, as The Independent revealed on Saturday, they have a plan to boost their own power on the NEC). After Labour’s unexpectedly strong showing on 8 June, the anti-Corbyn wing told me that their pre-election plan for a breakaway centre party was “dead.” Only three weeks later, they are talking about it again.

Two things have put it back on the agenda: the left-wingers’ moves and Corbyn’s stance on the EU. Sir Keir Starmer, the Shadow Brexit Secretary, has the most unenviable job in the Labour Party – bridging the divide between the Corbyn-John McDonnell camp, who do not want to die in the ditch opposing hard Brexit, and those Labour MPs who believe the election result means the party must step up to the plate and fight for soft Brexit.

Starmer’s painstaking work was interrupted when Umunna tabled an amendment to the Queen’s Speech calling for the UK to stay in the single market. Forty-nine Labour MPs voted for it, defying Corbyn’s line to abstain. It wasn’t really an anti-Corbyn revolt, more a marker for parliamentary battles to come on Brexit. But it has inevitably fuelled tensions between Labour’s two tribes. Starmer believed a consensus was possible and saw Umunna’s move as premature, since pro-EU Tory MPs were never going to rebel on the Queen’s Speech, but might do later.

If Labour does split, then Brexit would be the catalyst – if Corbyn does not move far enough for Labour’s centre-right. The seeds of a new party might just be planted in cross-party cooperation which steers the country to a more sensible, softer Brexit than the version May clings to but for which there is no majority in Parliament.

Despite headlines about Labour being “in meltdown” over Brexit, it is the Tories who are again torn apart over Europe. Labour should not allow its small differences to divert attention from that.