Jeremy Corbyn just got inside everyone else’s decision cycles. The Labour leader’s offer to lead a “strictly time-limited” government, to prevent a no-deal Brexit and to call a general election, has forced all political factions to react and led the news bulletins.

Amid the initial responses – which ranged from cautious to churlish – the bigger point has been missed. Corbyn’s gambit crossed numerous significant lines, both political and psychological.

First, it was a decisive rebuff to the leader of the Unite union, Len McCluskey. McCluskey is leading a rearguard action against Corbyn’s move to back a second referendum in all circumstances. Corbyn’s letter offered to make the second referendum the centrepiece of Labour’s election campaign.

Second, the actual offer was much more open than those close to Corbyn had been expecting. The letter says nothing about a Labour minority government seeking confidence and supply from other opposition parties. Instead it offers to begin negotiations for a “temporary government with the aim of calling a general election” and securing an extension of article 50 to do so. These words open the possibility of either an outright temporary coalition or a technocratic government.

Third, the letter says nothing about Labour fighting for its own particular desired form of Brexit – and was wise not to do so, because that prospect is dead.

The party’s policy, of course, remains officially confused. The shortest possible summary goes: “We’d vote remain in a referendum now but might – if our conference agrees it – go into an election fighting for a specifically Labour form of Brexit which we would then try to negotiate and after that put to a referendum, in which we would decide how to vote once we knew if the deal was any good.”

As all activists know, that is death on the doorstep, and having experienced it in the European parliament elections in May, few of us have the appetite to go on the knocker encumbered with it again.

Rebel Tories agree to meet Corbyn to stop no-deal Brexit Read more

Fortunately, we won’t have to – and to understand why, you need to understand the possible permutations, timing and sequencing of what happens next.

In early September the real action will not be around the confidence vote, but around an attempt by an expanded group of Tory rebels to use standing order 14 to take control of parliament’s agenda and introduce legislation forbidding no deal.

If Johnson were to defy parliament over that – for example by sabotaging the royal assent process – Tory rebel participation in a vote of no confidence would be both justified and, I am told, decisive.

Play Video 1:09 Jeremy Corbyn urges MPs to back Labour plan to block no-deal Brexit – video

There will be a lot of angst unleashed in the next few weeks over whether the Tory rebels, the Liberal Democrats and the Labour right could support putting Corbyn in office, but for the purposes of the Brexit outcome it does not matter whether it is him, Keir Starmer or some bespectacled crossbench peer nobody has ever heard of.

What matters is: what is the cross-party agreement over the function of that caretaker government? Should it, as Corbyn suggested, be limited to extending article 50 and calling an election. Or should it organise the second referendum itself, delaying a general election until the outcome of the referendum is known.

Under the first option, the election itself would become a proxy referendum on Brexit. Johnson and Nigel Farage would make it so. The Lib Dems, SNP, Plaid and Greens would probably do some kind of tactical voting deal. If Labour went into that election offering to restart negotiations with the EU, over the half-baked single market access deal once touted by Barry Gardiner, it could not win.

Not only that, increasing numbers of Corbyn-loyal backbenchers have made it clear that they will never vote for Brexit in the Commons in any form. So even with a small Labour majority by December, there would be no practical majority for renegotiating Brexit.

The arrow of time has narrowed the options, and the Trump administration has done the rest. The existential question for Britain now is whether it wants to be awash with chlorinated chicken and genetically modified food, and see the NHS privatised into the hands of US corporations – or whether it wants to be close to Europe.

So both for reasons of avoiding electoral suicide and in the national interest, Labour would have to fight a November election not just on the promise of a second referendum, but of remain/transform.

If we consider the preferred route of the Greens and Lib Dems – for a caretaker government that holds the referendum first, the election second – then Labour’s unicorn half-Brexit plan is even more firmly dead and buried.

The only way Corbyn gets to lead a “temporary government” that stops no deal is if all his own MPs back him, together with 10 ex-Labour independents, the SNP, Plaid, Caroline Lucas and at least a handful of Tory rebels.

But all his own MPs will not vote for him. So he needs a large number of Tory rebels – and that’s not going to happen either unless they get something that they want.

The temporary government we need is going to be formed on the terms of its most centrist supporters in the Commons – and that negates any possibility of a Labour government reopening negotiations.

Corbyn has shown bravery and skill with his letter. As his allies predicted, it immediately forced the Lib Dem leader, Jo Swinson, into a ludicrous position of refusal, which Labour strategists know will play very well for them on the doorstep.

But it is only the first move. The next move is to take control of parliament and, after that, a decisive no-confidence vote. But to stop Dominic Cummings’ plan to destroy our parliamentary democracy, there must be a definitive end to the idea of a “Labour Brexit”.

• Paul Mason is a writer and broadcaster on economics and social justice