You’re not being fired. Heavens, no. You and the company are merely going through what we call an “ambitious managed divergence”. The torture Brexit inflicts on the English language escalates daily, the latest indignity being the euphemism coined after the tellingly named Brexit war cabinet had an eight-hour session among the whiteboards at Chequers on Thursday. “Ambitious managed divergence” was the agreed description for the planned future relationship between Britain and the EU, a phrase so blatantly designed to stitch together two clashing positions you could see the seams.

Theresa May at risk of Commons defeat as Labour shifts on Brexit Read more

“Divergence” is there to satisfy the Johnson-Gove-Fox axis of Brexiteers, while “managed” is meant to placate the Hammond-Rudd rump of remain realists. “Ambitious” is the heroic attempt to dress up what is, in fact, a dollop of fudge chock-full of contradictions and likely to melt on first contact with the heat of trade talks in Brussels.

For it rests on the rather sweet belief that the 27 remaining EU states will allow Britain to converge where it suits us but diverge where we may gain a competitive advantage over them. This is the so-called “three baskets” theory, in which we divide our economy into three categories: one where standards and the like stay fully aligned with the EU, one where we have the option to diverge in future, and a third where we make a clean break.

Sounds appealing, right? And it certainly is – to Britain. But there’s no reason why the EU would even countenance it. For one thing, all 27 nations will have different views of which industries are too important to tolerate divergence and which they can be relaxed about: that will vary from member state to member state. According to Sam Lowe, trade analyst at the Centre for European Reform, what Britain is asking for is “institutionalised cherrypicking” – and no cherrypicking is the cardinal rule of the single market. Small wonder, then, that not long before the cabinet sat down to slow-braised Guinness short rib of beef, the European commission issued a document explicitly rejecting the three-basket approach. In light of that, “ambitious” is one way to describe the UK government’s approach. “Delusional” is another.

The hard choice the Chequers meeting ducked is the same one this government keeps ducking. Think of it this way. Britain will indeed get its own bespoke future deal with the EU, our most important trading partner which accounts for 43% of our exports. That deal will lie somewhere on the spectrum that includes the Norway model, which imposes high obligations in return for high access to the single market, and Canada, which is low obligation, low access. What is not on offer is a low-obligation, high-access deal.

Yet when the cabinet agrees that its preference is for “Canada plus plus plus”, it implies that such an arrangement – no pain, all gain – is what Britain may plausibly get. It’s a fantasy and an exercise in political fraud to keep hoodwinking business and the public into believing such an option is on the table. It isn’t. Britain will have to choose: we can either have few obligations or we can have good access to the lucrative market on our doorstep. We cannot have both.

As if that wasn’t enough, on Friday morning Jeremy Hunt reiterated the government’s opposition to any future customs union with the EU.

Which means all eyes shift to the speech Jeremy Corbyn will give on Monday, where he is expected to commit Labour to supporting such an arrangement. That matters, because it would take only a dozen or so Tory rebels, joined by Labour, to vote for an amendment on an upcoming – but now delayed – bill to defeat the government on this precise question.

Some in Labour are hailing the Monday speech as a big, even “seismic” shift. Others counsel caution, signalling that Corbyn will merely offer a “nuanced” advance from the existing position. Talk like that has led some Labour folk to worry that Monday will recall some of those set-piece Ed Miliband speeches on, say, immigration, where clarity was promised only for the text itself to require scholarly analysis and deconstruction. Others fret that Corbyn’s unscripted responses in the post-speech Q&A may contradict the official message.

There remains a vacancy at the helm, open for someone to step in

Perhaps the cool-headed view is that the Labour leader will indeed commit to a customs union, but that move shouldn’t be overhyped. Viewed one way, he could hardly do anything else. Thanks to that cross-party, backbench effort led by Chuka Umunna and Anna Soubry, the realistic prospect of defeating Theresa May’s government now looms: Corbyn could hardly stand in the way. (It was not a great look when, last November, John McDonnell found himself voting alongside Boris Johnson to defeat an amendment that would have protected the customs union.)

What’s more, an underrated intervention came earlier this month when Gerry Adams demanded that Northern Ireland stay in the customs union and single market in order to avoid a hard border. (A customs union is necessary for that, but not sufficient.) Corbyn was listening sympathetically to Adams more than three decades ago; it would be strange if he did not heed him now. Stranger still if he lined up with those hardcore Brexiteers who currently, and outrageously, suggest the Good Friday agreement can be discarded.

Also relevant is that the argument for constructive ambiguity – in which Labour’s fence-sitting on Brexit was credited with its relatively strong election performance last June – is losing traction. The closer October gets, by which time the terms of Britain’s future relationship with the EU will have to be known, if only in broad outline, the more incumbent it will be on Labour to take a stand.

All these are pressures on Corbyn, to which he is responding. But there is another path open to him. He can survey the current political landscape, in which Brexit – the most important and complex political project Britain has undertaken since the creation of the welfare state – is oddly orphaned.

May has proved that she cannot lead on it, caught between competing factions of her divided party. Backbenchers are doing noble work, seizing the initiative where they can. But there remains a vacancy at the helm, open for someone to step in and get a grip on this most fundamental question – setting out clearly and concretely a plan for our European future. After that unexpected result in June, Labour’s most fervent supporters hailed Jeremy Corbyn as “the real prime minister”. On Monday, he has the chance to act like one.

• Jonathan Freedland is a Guardian columnist