He called it all “mumbo jumbo” in his destined-to-be leaked after-dinner speech. The foreign secretary was mocking the Treasury’s anxiety to keep frictionless borders. “Yeah, yeah, of course,” he conceded. No deal does mean that, at borders, “there will be some dislocation … some bumps on the road”.

Bumps? Here are just a few for MPs to remember on Tuesday as they vote on the EU withdrawal bill, before blundering another step nearer the precipice.

PM resists calls to sack Boris Johnson over Brexit remarks Read more

Leaving the customs union and single market turns out to be a thousand times tougher than anyone imagined. Each week new nightmares emerge that no one saw before the referendum. Brexiters deliberately deceived with breezy promises of fantasy trade in distant Shangri-Las, but remainers knew little of the true perils.

In a 45-year bonding inside the EU, our jobs, lives and economies have grown together like a grafted tree. In the warp and weft of our mutual development it turns out to be impossible to unpick the EU threads without destroying the fabric of our intertwined institutions.

Pick at random from some 40 EU agencies relying on each others’ expertise and resources. As each is exposed to the light, the Brexiters protest, “Oh, we’ll stay in this one”, or “We’ll make a special agreement with that” – with no precedent. Nothing has been fixed, with under 300 days to go. The medicines agency departs to Amsterdam, shedding expertise that keeps big pharmaceutical companies here. Recently these businesses protested at the lack of an interim deal to prevent the 45m medicine packs that the UK exports each month to EU and EEA countries from requiring customs checks on both sides of the Channel.

Leaving Euratom disrupts access to medical isotopes – and the whole nuclear industry. Don’t assume we will stay in the European aviation safety agency, guaranteeing joint flying. Must we leave the European Investment Bank? In the 18 months before the referendum it lent us €13.5bn (£11.9bn) cheaply for 74 affordable housing and capital projects – new trains for Merseyside, €1bn for housing in Wigan, Scarborough, Bradford and elsewhere. Since the vote, the UK has been lent just €3bn, due to Brexit uncertainty. Nothing is agreed on security, on Europol or the European arrest warrant. On farming, the National Farmers’ Union warns the customs union is not enough for exporting our beef and lamb to the EU without friction. And ask the fruit and veg growers about their vanishing EU pickers.

Monday saw the largest manufacturing fall in five years. Many carmakers are seeking alternative post-Brexit plans. A Mini has parts made in Austria, Hungary, Poland and France, plus hundreds more supply lines criss-crossing borders in hours. First Theresa May promised they would work “within the single market”, then outside but with “frictionless trade” and now there is only her unfathomable, “as frictionless as possible”.

Pondering Boris Johnson’s bumpy road, I talked to James Hookham of the Freight Transport Association (FTA). He sees no plan for borders, though “the French are hiring new fast-track customs officers expecting checks”. Every extra two-minute delay for trucks at Dover causes a 20-mile motorway tailback and, he says, “No one voted for paralysis.”

No-dealer Jacob Rees-Mogg claimed on Monday that there would be no hold-ups, as the UK need set no tariffs or checks. But this breaks WTO rules. (Will we join the few – Bhutan and Turkmenistan – outside the WTO?) The FTA has still not been told if the industry can keep its 43,000 EU drivers, or whose qualifications will be recognised. These are not bumps but craters.

The Johnson-Moggites wave all this away. Common sense will prevail, they say: a quality unknown to them. Johnson wishes Trump was in charge: “He’d go in bloody hard. There’d be all sorts of breakdowns, all sorts of chaos … But actually you might get somewhere.” These no-dealers have no answers, only bluster, while EU negotiators are led by a clear-cut rule book we helped draw up – but that’s all mumbo jumbo now.

On one thing Johnson is right: “We will end up locked in orbit around the EU.” Look at each erupting problem, each agency, each type of trade: the gravitational pull of our great neighbouring trading partner is far too strong to resist. If pusillanimous MPs chicken out this week, by October the only commonsense course is for parliament to tell hard truths we barely knew before. Then perhaps the country can choose to step back from Brexit, when no deal or a miserable, rule-taking, outsiders’ deal will make a mockery of taking back control.

• Polly Toynbee is a Guardian staff columnist