Historians will debate the reasons for the complacency that descended on the British in the first months of the 2020s. Had their government duped the nation into ignorant passivity? Were they really as stupid as they appeared to be? Nothing had been settled. The pain was yet to come. Yet they behaved as if they believed Boris Johnson when he said he could “get Brexit done”. And, as I’m certain the historians of the future will say, believing Boris Johnson never ended well.

A few causes of our torpor appear obvious. The Conservatives won a handsome majority. Brexit bored the public rigid. The opposition was hopeless. Journalists weren’t doing their job. The prime minister was thus free to announce: “Now we can put the rancour and division of the past three years behind us and focus on delivering a bright, exciting future”, and not be met with derisive laughter.

Yet the delusions that follow are anything but obvious. As the clock chimes 11 on Friday night, we can, apparently, build high-speed rail lines, reinvigorate the north, bail out a regional airline and let a thousand bus services bloom. We can tear up our economic model without having the smallest idea what to put in its place.

The listless acceptance extends to those who believe that leaving the European Union is an act of monumental folly. Brexit’s inevitability, the possibility that we are in for another decade of rightwing rule, is leading opponents of the status quo to retreat into private life, as the defeated so often do. Perhaps they are almost grateful for the chance to concentrate on their friendships, family and love affairs: these are in the end what matter most to everyone except obsessives.

Aren’t you sick of an argument about a subject no one except a handful of zealots cared about before 2016?

On this reading, the country has not been wholly deceived by Johnson and his propagandists. The British are just exhausted. In a piece for the Parisian news magazine, L’Express, the French journalist and historian Agnès Poirier interviewed psychiatrists dealing with voters who had looked on appalled as Britain made a disastrous choice. They were “devastated, angry, depressed, betrayed and ashamed”, as a psychological study of Remain supporters put it. Brexit allowed the old to enforce their worldview on the young and broke ties between the generations. “My patients talk about the impossibility of mentioning the subject in family, to avoid clashes. In extreme cases, they have cut ties,” Dr Ian Martin, a London psychiatrist, said – a story I have heard several times myself.

“It’s not the fear that kills you but the hope,” runs the cliche. And now all hope of a second referendum or a change of government has gone, a kind of liberation follows. You can just sigh, move on and patch up differences. What else is there to do?

Perhaps many will be relieved. Poirier repeats the echoingly grim phrase the French socialist Léon Blum used to describe the decision by France and Britain to allow Hitler to dismember Czechoslovakia at the Munich conference of 1938: a “lâche soulagement” – a cowardly relief. Selling out Czechoslovakia was shameful, but Blum, who had campaigned for peace, could tell himself that at least it avoided war in Europe. Do you feel a lâche soulagement of your own? Aren’t you sick of an argument about a subject no one except a handful of zealots cared about before 2016?

The millions who think they can now avoid the bitterness of 2016-19 will find that it has just been postponed

Wouldn’t it be more truly British to come together, let bygones be bygones, and make the best of it? I don’t see how you can if you are one of the three million EU nationals in Britain or 1.5 million Britons in the EU who have seen their sense of who they are and where they belong torn to shreds. But if you face no immediate stresses, the temptation to walk away is seductive.

The Munich agreement did not avoid war, it merely postponed it for a year. Likewise, the millions who think they can now avoid the bitterness of 2016-19 will find that it, too, has just been postponed. You may not be interested in Brexit but Brexit is interested in you.

The hard break the government is proposing as the only way to leave the EU without following EU law will be a direct attack on the pharmaceutical, chemical, aerospace, food processing, farming, fishing and car industries. Businesses that rely on the frictionless movement of goods will suffer. The absence of regulatory checks and arguments about the source of components and applicable tax rates is essential for their health, just as the absence of border checks on perishable food is essential for fresh food and fish exports. Hundreds of thousands of jobs and everyone’s living standards are at stake. The Food and Drink Federation said last week that the Johnson administration’s policies sounded like the “death knell” for frictionless trade with the EU and were likely to cause food prices to rise.

You can tell we are in a state that borders on the catatonic when Sajid Javid responded by telling the Financial Times that some businesses would indeed suffer. It was a welcome outbreak of honesty from a dishonest administration. But what an admission from a chancellor of the exchequer charged with protecting the economy.

As telling was the indifference with which his dereliction of duty was greeted. The liberal elite, the chattering classes, the remoaners, call them what you will, once worried about the fate of car workers. Every serious study of the consequences of Brexit has shown that it will hit the old manufacturing regions of the north-east, Wales and Midlands hardest. London will be all right, as London always is. Yet at the moment they need support, they will be met with indifference. They will hear educated voices say that they voted for Brexit in 2016 and then voted for Johnson in 2019. They were warned and chose not to listen.

I fear that the most damaging effect of the languid complacency that has infected the national mood is the collapse of any notion of solidarity. The most characteristic gesture of Brexit Britain will be a shrug of the shoulders.

• Nick Cohen is an Observer columnist