Ring out the bells! Brexit is done today, as promised. Or almost done, as first and second readings are dashed through the Johnsonised Commons, disregarding the notion a bill should be published first to allow at least a week to scrutinise it before voting on the second reading. But to hell with rules, precedents, procedure. From now on, the will and whim of Boris Johnson is iron law.

By 10 January the withdrawal agreement bill will be through the Commons, and through the Lords in good time for Brexit by 31 January, fulfilling the only election pledge that mattered. Thereafter, the word Brexit is to be banished from his kingdom, Johnson proclaims. (No chance.) Parliament will lose any right to know anything about the progress of the free trade deal that will cement the country’s future for decades. Nor will there be any vote on its final terms.

It is an opposition’s duty to expose every weakness, to shine a light on perils ahead and plot an alternative course

Under the Constitutional Reform and Governance Act, Johnson could get away with agreeing a treaty in private, with no public news on its progress, allowing one day in parliament to discuss his deal or his no-deal without a vote. And that’s that: ultra-hard Brexit or betraying-the-ERG-soft or no deal at all, no one can stop him now. The same will be true of any treaty he strikes with Donald Trump.

Except that’s not how it will actually be. The progress of talks will leak daily, true or distorted versions stirring fury with one side or the other, one industry or another. The government will deny damaging stories that turn out to be true. Nothing will be resolved until everything is resolved, which means nothing – no deal – is a dangerously plausible result.

Whatever Johnson does, he cannot keep all of his Brexit promises, as gigantic hurdles stand in his way. The most impassable are fisheries, agriculture, finance and Northern Ireland. No fixes and fudges will let him bluster through these. One is of the gravest economic importance, the others are of little financial value but stand at the beating heart of everything Brexit stands for – nation, flag, heritage, identity and independence.

Start with the one that is least important economically, but has the greatest emotional tug. Fishers were promised “instant” escape from the common fisheries policy. The industry provides just 0.5% of GDP, but 100% of the nation’s romantic seafaring identity. Total control over our own waters within a 12-mile limit is what the fishers think they were promised, getting back all the quota taken by EU boats: UK boats catch only 40% of tonnage. But here’s the real catch – they sell 80% of it to the EU and we import 70% of the fish we like from the EU. The French, Dutch and Spanish feel as passionately patriotic about the seas as we do. No deal on anything without a fisheries deal, they say. They will bar Scottish smoked salmon, which alone is worth more than all other fishing and fish processing. So Johnson must decide – will he sell out the fishers to the vital interests of our pharma, finance or airline routes?

The 80% of our economy devoted to services will get no deal, with a bare-bones, goods-only free trade agreement fixed in 11 months. This will be a slow frog-boiler, banks and finance slipping away quietly, many new HQs already set up in Frankfurt and Paris, new investment not arriving. Predictions vary from a 2% to a 7% loss to GDP.

The third gigantic boulder in Johnson’s path is still Northern Ireland. The border down the Irish sea, with Northern Ireland in the customs union and the rest of the UK out, will never be accepted by unionists. In today’s latest ONS figures, NI came off worst, again: its GDP fell by 1.1% last year. Its industry tussles with what rules and checks will mean, while loyalists warn against Johnson’s “betrayal bill”.

Trade talks may take place “in secret”, but Johnson will have no hiding place from any impassable Brexit obstacles. He will be obliged to break impossible promises. It hardly matters where the opposition stands – these contradictions are in-built, recklessly created by his foolish posturing. A soft Brexit, staying closely aligned to the single market and customs union, would resolve most of them, keeping EU rules and regulations. But Johnson seems resolute against that path, a populist following the country’s choice of romance over economic well-being.

Labour must not just accept Brexit but embrace it | Larry Elliott Read more

Forget the PM’s “golden age” balderdash: these Brexit pigeons will come home to roost, sooner not later. If Labour wants any role in the country’s future, it has to carve out a clear path on what kind of Brexit the UK needs. Fully accepting Brexit will happen doesn’t mean kowtowing to a Johnson Brexit. Lexiters on Labour benches, their position expounded by Larry Elliott, may be tempted to embrace any Brexit: after the shock of losing those old Labour Brexit votes, silent capitulation could look tempting.

But it is an opposition’s duty to expose every weakness in government policy, to shine a light on perils ahead and plot an alternative course. If complicit now, what can Labour say when Brexit wreaks economic havoc, emptying the treasury of funds for spending on parched public services?

The party needs a fearless leader who can be forensic in charting the downward drag of Brexit on every aspect of Britain’s fortunes over the next five years. Of course if, against all odds, Brexit turns out to be as “fantastic” as Johnson and the Lexiters promise, it won’t matter what Labour has said. The party will be dead as a door nail for an aeon.

• Polly Toynbee is a Guardian columnist