Today parliament returns, led by the most dangerously incompetent and decadent government in modern times. This parliament will seal the country’s fate permanently and, on current form, fatally: nothing in the conduct of Brexit suggests any understanding of the cataclysm ahead. Instead the summer has seen only callow jockeying for position between would-be Tory leaders of unbelievable unsuitability.

Their frivolity was summed up by David Davis dismissing EU negotiator Michel Barnier as “silly”. But silliness is now Britain’s official position. Those who holidayed in the EU this summer will have met that amazement from taxi drivers, bartenders, students and old-timers alike: they think we are mad. And so we are. What else can they make of a country with Boris Johnson as foreign secretary? According to Sunday’s Survation poll, he is favourite to take over from Theresa May, with Jacob Rees-Mogg in second place. As if despairing of politics, many voters seem to prefer any alternative reality to the one we face.

EU Brexit negotiator: UK demands on single market are impossible - Politics live Read more

In just a year the deal must be done, in time to be ratified by the 27 nations by March 2019. Our government has approached it like a bunch of England football fans, shouting: “Who won the war?” Supposedly sober politicians boast loudly that they need us more than we need them: “We hold all the cards!” Those with delusions about Britain’s importance should note that in Sunday’s election debate between Angela Merkel and Martin Schultz, Brexit was not mentioned once. The EU faces many crises – migration flows across the Mediterranean, Ukraine at war with Russia, Donald Trump and North Korea – and the relentless burning and flooding of our planet.

Of course, they’d like Brexit resolved painlessly, but frankly they’re not that bothered. Some are bemused: Germany’s ambassador to France pondered at a public meeting last week: “I am waiting for the big free-trade deals that a small island can conclude to its benefit with the rest of the world.” Every meeting between our beseeching ministers and potential trading partners in Japan, India or the United States leaves us asking that same question.

Why can’t Barnier be more “flexible” and “imaginative”, David Davis asks, revealing he hasn’t grasped the basics. The memorandum signed by both sides at the outset clearly spelled out the EU 27’s overriding goal: “European integration has brought peace and prosperity to Europe and allowed for an unprecedented level and scope of cooperation on matters of common interest in a rapidly changing world. Therefore, the Union’s overall objective in these negotiations will be to preserve its interests, those of its citizens, its businesses and its Member States.” That’s it. Protecting the EU and its hard-won single market and customs union matters more than any British deal. That means no unpicking, no bending the rules, no “imagination”: it’s our choice to stay or leave.

Play Video 1:11 Jeremy Corbyn: Brexit transitional deal is ‘important for jobs’ – video

The UK’s realm of fantasy unravels embarrassingly fast. Only two weeks ago one policy paper proposed an “innovative” and “unprecedented” system to abolish customs checks by electronically tagging goods, cleverly passing on any dues to the EU. It was pure magic, as the EU protested. Only a fortnight later Davis had to take it off the table because no one has invented it: “It was a blue sky idea”, he said with that jovial nonchalance whose charm is fast wearing thin.

The result? If we leave the customs union and single market, it’s a hard border, he admitted, with all goods checked and declared. For Northern Ireland, that’s a disaster – with no ingenious way round it, none at all: all the border constituencies are Sinn Féin seats, now facing hard border posts. Brexiters have a habit of brushing away such impossibilities as mere flies in their ointment, but there is no ointment, only flies. I have interviewed those in an overstretched border force who say already they often abandon customs posts to cope with passport queues: will it take gridlock on both sides of the Channel before Brexit doubts penetrate? Or Ryanair’s Michael O’Leary proving right, that EU flights will stop? Not a week goes by without some new sign of imminent Brexit-caused decline.

Their frivolity was summed up by David Davis dismissing EU negotiator Michel Barnier as ‘silly'

The tumbril bearing the EU withdrawal bill rolls in for its second reading on Thursday. Dominic Grieve, the most influential Tory objector, writing in yesterday’s FT, warns of the bill’s draconian Henry VIII powers: “The electorate did not vote to ‘take back control’ to see our domestic constitution dismantled.” Vital amendments will be put, but experience warns that Tory rebellions have a habit of much bark and little bite.

Labour MPs still pinch themselves at finding they are the parliamentary grownups now, watching an infantile government throw the nation’s toys out of its pram. How did it happen that the most radical Labour opposition in years is the sober-sided sensibles, the only hope for rescuing the country? Keir Starmer has steered the party adroitly towards staying in the single market and the customs union during a lengthy “transition”: that’s the place to be when no one can say in this wildly volatile political climate who will be in power, or what the country needs in five years’ time. Astonishingly, the party is growing more united by the week, as Starmer sticks it to Davis today in the Commons, taunting him for his fantasies being forced to give way to brutal reality.

Play Video 0:39 ‘We can’t be blackmailed’: Liam Fox issues warning to EU over Brexit - video

What will persuade the people to rethink? Barnier keeps warning that leaving the single market will have “extremely serious consequences”, and he’s right that that they haven’t been explained to those deceived by Brexit delusionists over the decades.

But I hear too many remainers itch for disaster. Some yearn for the great “I told you so” vindication as trucks stack a hundred miles up on the M2 and “just-in-time” manufacturing and service industries grind to a halt, with unemployment soaring. Secretly they want dire consequences for all to see, to stop Brexiters claiming for ever more that staying in the single market, customs union and European Economic Area was a betrayal of the people’s will.

Never wish for political revenge, however. The great hope must be that we swerve at the last moment and avoid the worst. When countries decline and fail, they don’t turn nicer. We are lucky that no serious demagogue has yet seized the chance of this perilous, fickle mood: so far we are only threatened by a leadership of jokers.

• Polly Toynbee is a Guardian columnist