Theresa May never cast her deciding vote nor even expressed a view at last week’s warring Brexit cabinet committee meetings, deliberately constructed as a five-a-side stand-off. Opening the session on Ireland and immigration, the prime minister reportedly declared, “We don’t need to decide anything today.” And so they didn’t, again. Warfare resumes next week at a Chequers away day. Nineteen long months after the vote, EU negotiators tap their fingers in irritation as Michel Barnier reminds us that “The time is short, very short.” The 22 March deadline for agreeing a transition deal may be missed, derailed by the Mogglodytes’ objection that it makes us rule-taking “vassals”.

There is nothing new for either side to think or say. Brextremists stick their fingers in their ears at each revelation of ill-effects. Take the past few days: we have learned of fruit and vegetables being left to rot in the fields for lack of foreign EU labour, and that road haulage permits will be strictly limited once we depart. Lack of EU nurses worsens the 40,000 NHS nursing vacancies, and the UK will be last to get new medicines. Who knew 90% of official vets in abattoirs, some of whom are already leaving, were EU citizens? Public health laboratories at ports warn they will not be able to cope with import checks, as they too are staffed by EU citizens: food will rot on the quayside. Who knew that Ofcom, on behalf of the EU, checks most broadcasting arriving from non-EU countries? Brexit risks thousands of those jobs.

Day by day, more unconsidered mishaps emerge. Look at last week’s cabinet report showing a hard Brexit would wipe out 16% of economic growth in the poorest areas. Yes, that’s still phoney-war speculation – but right now, despite the weak pound, the trade deficit is widening as imports increase faster than exports. UK growth lags further behind the EU and the US. It was top of the G7, now it’s bottom.

Great new trade deals? Liam Fox gallivants around the globe trying to secure the same EU deals with 60 countries that we lose when we leave – and he finds they have us over a barrel: South Africa demands we accept a flood of agricultural produce, threatening our own farmers. India wants the visas May refuses. Never mind, open up to unilateral tariff-free trade, say Rees-Moggites. They quote the Brexit economist Patrick Minford, who agrees that free trade would kill off our farming and manufacturing, suggesting we stick to selling financial services. That certainly wasn’t their message at the referendum.

I hear that Boris Johnson, if faced with unpalatable facts, has a habit of fluttering his fingers in front of his face, shutting his eyes and going, “Na na na na” to blank out any of his officials bearing bad news. That’s the only way these dishonest fantasists can keep going. Yet he is to make a speech on Wednesday to “unite the country” and appeal to remainers. Good luck with that.

The border conundrum can only be resolved by forcing May to abandon her contradictory red lines

But there is one great question: Ireland. The Brexiteers avoid mentioning it, because Ireland is their roadblock. The border is marked by memories of British bad faith that have been gradually healing over 20 years of peace. What a strange irony if Ireland ends up saving us all from ourselves. The border conundrum can only be resolved by forcing May to abandon her contradictory red lines – no customs union, no single market, no European court of justice – and no hard border.

Barnier says Northern Ireland alone could stay in the customs union and the single market. Naturally, the SNP jumped up to say “me too”. Maybe the Brexiteers are destructive enough to accept an end to the UK as a price worth paying? But the DUP they depend on rejects outright any border with the rest of us.

In the cabinet committee the Brexiteers reached again for technology for the border; some mentioned drones. But CCTV or automatic number plate recognition cameras would be vulnerable: Northern Ireland’s chief constable warned last week that any such technology would be paramilitary targets. Move the border to Belfast, was one Brexit brainwave, but wherever they are, border hangars for lorry customs checks will be emblems of an end to Good Friday peace.

The Irish stand in sadness, dismay and puzzlement. I spoke yesterday to the Irish ambassador, who observes government disarray daily and waits for a sign. He points to the withdrawal agreement, where paragraph 49 is carved in stone. On the border question it says: “In the absence of agreed solutions, the United Kingdom will maintain full alignment with those rules of the internal market and the customs union.” There are no other agreed solutions – none. Clarity is needed fast, says the ambassador, “Paragraph 49 is the failsafe.” Barnier is only obeying European council instructions: the EU27 are rock-solid on their no hard border promise.

“Full alignment” for Northern Ireland meets its parliamentary test this month, when amendments to trade bills call for staying in the customs union. It would be unthinkable for Labour not to vote for that: its own upcoming away day will certainly agree. Otherwise it sides with Rees-Mogg, Iain Duncan Smith and John Redwood. What’s more, “full alignment” will mean near–as-dammit staying inside the single market too, which is just as vital for keeping the Irish border open.

The shadow Brexit secretary, Keir Starmer, says: “No one has explained how the border commitments can be kept unless a customs union with the EU is on the negotiating table and the final deal delivers the benefits of the single market.” Never mind the finessed language, watch that turn into a resounding Labour vote when the crunch comes, as Anna Soubry and Ken Clarke rally Tory rebels.

May dares not see off her ultra wing, but parliament looks set to do it for her. The anvil on which a soft Brexit is forged will be Ireland, because there is no other option. Despite history, it stands to be the United Kingdom’s saviour.

• Polly Toynbee is a Guardian columnist