In one of his most famous and controversial bons mots, the historian AJP Taylor claimed that the first world war was “imposed on the statesmen of Europe by railway timetables” – the fixed and fiendishly complex transport schedules that underpinned the military mobilisation plans of the great powers. A century after that terrible conflict’s end, I wonder if the authority of the timetable is going to work its mischief once again. Though Brexit can scarcely be compared to a great global conflict, it is increasingly obvious that – whatever form it takes – it will be worse than the status quo.

Only the most flame-eyed ideologues seriously believe otherwise: the kind who would have declared the sighting of the iceberg from the Titanic to be Project Fear. Regrettably, a great many others in the political class have succumbed to wilful blindness, choosing the craven option of quiet complicity, rather than the harder path that a public recognition of reality would entail.

They claim only to be enacting the “will of the people”, expressed in the 2016 referendum, as though they have no corollary responsibility to respond as representatives of their constituents to all that has emerged in the past two and a half years about the likely form and consequences of Brexit.

The whole ridiculous process is now governed by the ticking of the clock. We must leave on 29 March 2019, at 11pm. That, in turn, means that the deal – if it is reached – has to be signed off in the very near future by the cabinet and then by parliament.

No such agreement, of course, has yet been struck with Brussels. Theresa May’s senior ministers are far from consensus on what would constitute an acceptable plan. And the Commons resembles a cacophonous gathering of factions, all of them engaging in the narcissism of small differences as well as more principled position-taking. Yet over them still looms the clock, doing its merciless work, draining the argument of reflection, caution and historical perspective.

In this context, the resignation of Jo Johnson on Friday was much more significant than his brother Boris’s in July. May had long contended with the possibility that cabinet Brexiteers would quit over her compromises with Brussels – indeed, she still does so, conscious that Andrea Leadsom, Penny Mordaunt and Esther McVey are watching her like a trio of hawks, ready to fly away from the table as soon as she hands too much to the EU.

This was always in the Brexit script: the outraged departure of ministers convinced that the dream of 2016 was being betrayed. But Johnson’s decision to quit as transport minister is much more significant: the first time that a senior remainer, a minister sometimes tipped as a future Tory leader, has left the government over our prospective exit from the EU. And he did so because he believes, correctly, that the prime minister is presenting the nation “with a choice between two deeply unattractive outcomes, vassalage and chaos”.

The prospect of a no-deal exit – for which ministers are now preparing with the weary compliance of regional civil defence authorities in the cold war – is manifestly appalling. And what May calls a “deal” is, no less clearly, just a worse version of our existing relationship with the EU.

In this respect, Johnson’s departure represents a fatal convergence between remainers and leavers, in the recognition that it is plain stupid to be an EU rule-taker but not a rule-maker. As the former education secretary Justine Greening told the Observer: “The parliamentary deadlock has been clear for some time. It’s crucial now for parliament to vote down this plan, because it is the biggest giveaway of sovereignty in modern times.”

Remember that these are the words not of Jacob Rees-Mogg or David Davis but a campaigner for Britain’s continued membership of the EU. Like the younger Johnson, Greening insists that “the government and parliament must recognise we should give people a final say on Brexit”. Quite right, too.

What remains mystifying – and depressing – is the extent to which so many notionally intelligent politicians believed that the negotiations would lead inexorably to a happier outcome. Naturally, they were warned, at first politely, that their fantasies were just that. As long ago as January 2017 (when his country held the rotating presidency of the EU), Joseph Muscat, the Maltese prime minister, told the UK: “We want a fair deal, but that fair deal needs to be inferior to membership.”

This was, and remains, common sense. Yet the magical thinking of 2016 continued to hold sway: the EU needed us more than we needed them; provisional free trade deals with the rest of the world would fall into our lap as exit approached; the nation would exult in a collective surge of imminent emancipation.

Only now – in the symbolic form of the intractable Irish border question – has the grim reality of the process started to be more generally acknowledged. You cannot be both in and out of the EU (on this, the hard Brexiteers are quite right). You cannot have a porous Irish border unless Northern Ireland, or the whole UK, stays in the EU customs union until the matter is resolved. And the power to end this “backstop” cannot be reserved, unilaterally, by the UK.

All the logic – remember that? – points to an extension of article 50, more talks and a people’s vote. Much more probable is a political collapse in which May is ousted, or a general election is forced by parliamentary impasse – or both.

Is Labour ready to take the strain? Because all this is going to happen very soon. Until then, the Brexit train grinds on to nowhere; it is not the people that are sovereign, but the timetable.

• Matthew d’Ancona is a Guardian columnist