Margaret Thatcher once said that Northern Ireland is “as British as Finchley”.  This is true.  But it did not follow then that the province was governed in the same way as her constituency – direct rule was in place – and it is governed even less like it now.  Furthermore, one of the main consequences of the Blair devolution settlement is that neither Scotland nor Wales are governed like Finchley either.  And the localism upheaval under David Cameron, complete with an uneven dispersion of new powers, has ensured that English local government is now mind-bendingly diverse.

But neither England, Scotland nor Wales have a joint Ministerial council, legitimised by an international agreement, “to bring together those with executive responsibilities in Northern Ireland and the Irish Government, to develop consultation, co-operation and action within the island of Ireland – including through implementation on an all-island and cross-border basis – on matters of mutual interest within the competence of the Administrations, North and South.”  Those words are from the Belfast Agreement.  And in them is to be found a cause of yesterday’s Brexit talks volte-face.

The Republic and Northern Ireland trade less than a country and part of another that share a land border might be expected to do.  But some parts of the economies of the two are effectively integrated – one of the fruits of the Agreement.  The classic example is the single electricity market.  What happened during the talks yesterday is not fully clear.  But it is evident that the Government sought to build on those all-island and cross-border arrangements to solve the problem of how to deal with our only land border with the EU post-Brexit.  The common position of the parties to the negotiations is that they want it to continue as it is to the fullest extent possible.

The Irish Government seems to have wanted “no regulatory divergence”.  This would effectively mean continued Single Market and Customs Union membership for Northern Ireland.  That, in turn, would inevitably lead to one of two outcomes.  First, all of the UK remaining in both, contrary to Theresa May’s established position.  Or, second, Northern Ireland alone remaining in both – leading to an east/west border rather than a north/south one.  It is no exaggeration to say that such a change would be a significant step towards a united Ireland, and one that would threaten to unravel the jittery settlement that the Belfast Agreement formalised.

The Government appears to have pushed instead for, and got, an agreement on “continued regulatory alignment”.  At this point, one must reach for one’s dictionary.  Alignment and membership are not the same – which will have been precisely why Ministers pushed for the word’s inclusion in the draft text: indeed, the first word implies some difference.  As we say, what the Government proposed yesterday is not completely evident.  But one version is that the Prime Minister sought to agree such alignment only for those areas in which Irish north-south co-operation run – and, crucially, to extend them to the UK as a whole, thus ensuring no “east/west border”.

It ought not to be objectionable to the DUP to continue what it has been doing since Ian Paisley became First Minister – namely, arranging certain parts of the province’s affairs on an all-island basis.  None the less, we have a certain sympathy for Arlene Foster and her colleagues.  They do not appear to have seen the draft text.  The Prime Minister’s account of it to them may not have been clear, and there may be elements to the draft which have not yet been publicised, but which the DUP found objectionable.  Above all, Foster and her party have to watch their backs against those who would accuse them of selling out – a potent charge in Northern Ireland.

The old saying has it that Russia is never as strong as it looks, and never as weak as it looks.  Old peace process hands, looking back on the run-up to the Agreement, might offer a parallel: the talks between the two governments and Northern Ireland’s parties were never as near collapsing as they looked and never as near completion as they looked.  They lurched from joy to despair (depending on one’s point of view).  So it was yesterday afternoon.  One moment, Diehard Remainers were damning May for embracing the Single Market; the next, they were damning her for not doing so.

It may be that the DUP, having made their protest, wring concessions from the Prime Minister – perhaps including yet more money for the province from what Paul Bew has called “the Unknown British Taxpayer, the true hero of the Troubles”.  Foster would then be able to claim victory.  The talks would move to the next phase – and to the next round of frustrations, impasses and quarrels.  In the meanwhile, though, May would have “reversed the narrative”.  Her qualities of doggedness, caution and reticence, so lampooned in the Westminster Village since last June’s election setback, would be hailed as the embodiment of the bulldog spirit (very briefly).

That is the optimistic reading of what has happened and could happen.  The pessimistic one is no less likely and much more alarming.  It is that May’s offer yesterday moved her Government closer to an EEA minus-type settlement than a Canada-plus style one.  This would be compatible with the letter of Brexit, but not with the spirit – and would make any sensible new system of immigration control impossible.  And we do not yet know precisely where she is on ECJ jurisdiction in relation to EU nationals.  Such a shift has not been agreed by the Cabinet.  It would be objectionable to a big slice of Tory MPs and Leave voters.

How would Boris Johnson react to such a development?  Michael Gove?  David Davis?  Or Liam Fox, whose department could be deprived of much of its purpose?  Yet if part of the Conservative Parliamentary would pull one way in such circumstances, much of the Commons would pull the other, including many Tory MPs.  One logical way of proceeding, if no agreement is reached to move to the next stage of talks, would be to prepare for No Deal, as the shorthand has it, and to take the WTO route.  But some Ministers believe that there is no Commons majority for this course, at least at the moment.

The Prime Minister has got used since last June to living dangerously.  This morning, she is doing so more than ever.  The coherence and operability of her Government is under a new and sudden strain.  One part of the Conservative Party will want to stand with the DUP.  Another will yearn for compromise – and EEA minus.  This, potentially, is the stuff of which leadership challenges are made.  Worse, the DUP’s MPs could walk away from the confidence and supply deal altogether.  That would not necessarily mean an election, since the Fixed-Terms Parliament Act is in place. But remember: it didn’t prevent a poll last summer. No pressure, then, Theresa!