IT is the great paradox of the Brexit crisis that an affair that began on a wave of reactionary English nationalism has run into the political sands of Ireland’s long struggle for freedom. John Bull’s “other island” has emerged this week as the stumbling block to getting a Brexit deal passed the embittered factions of the Tories and their DUP allies. This impasse can only end one way: in the six partitioned counties of Northern Ireland exiting this (dis)United Kingdom and merging – perhaps in stages, perhaps faster – with their 26 fellow counties in the Irish Republic.

Start with a truth rarely admitted: the UK was created by force, deceit and bribery – it was never a voluntary affair. And non-voluntary associations always break up eventually.

Wales was conquered by Edward I between 1277 and 1283, though it took virtually another half millennium before the Celts in the dark Welsh valleys were forced into quiescence. The incorporation of Wales by the English state began as a feudal land grab and ended by littering the valleys with coal slag heaps.

The oft-neglected Cornish provided the rich mineral wealth that funded the English state and its foreign adventures, right down to modern times. Time after time, Cornish miners rose against their exploiters across the Tamar River. In 1497, they opposed new taxes imposed by Henry VII to fund his war on Scotland. In 1645, Richard Grenville rallied popular support in defence of ancient Cornish feudal rights and independence against Cromwell’s Ironsides imposing the rule of England’s new-fangled yeoman capitalists and London bankers.

Scotland was a tougher nut to crack. But in 1707, the dominant Scottish feudal aristocracy decided that an incorporating union would best protect their interests against an angry Scottish peasantry and uppity new urban bourgeois. The Union left Scotland politically in the hands of a greedy, subservient petty bourgeoisie and an aristocracy that happily replaced peasants with sheep, and baronial piles with London townhouses. There was a brief flowering of Scottish industrial capitalism in the 19th and 20th centuries. But Scotland’s industrialists preferred protectionism and subsidies to building their own state, and they withered away when London had no further use for them. Scotland, with its creative people and vast natural resources, was looted and despoiled – then told it was too poor and too stupid to manage itself.

Then there’s Ireland – the one part of the British state that regained its independence and dignity, in December 1921. At root, the struggle was a peasant war against a foreign land-owning class. Like all such wars, it was ferocious and merciless. The British ruling class fought back with the same sort of inhumanity and mechanised brutality it used in other colonial wars. As a result, the duplicitous British state held on to a part of Ireland after 1921 – the bit with heavy industry and rich farms – and continued to rule through a narrow Ulster oligarchy comprised of super-rich industrialists, smug landowners and a tiny Protestant skilled workforce. The latter were split from their unskilled Catholic proletarian brothers and sisters through religion and petty privileges.

The result was a Protestant Bantustan which ruled itself at Stormont from 1921 to 1972, as well as sending a large contingent of Unionist MPs to bolster Tory ranks at Westminster. To retain power, the Protestant oligarchy gerrymandered constituency boundaries for Westminster and local councils, deliberately denying voting rights and council homes to local Catholics. Far from the UK achieving universal adult suffrage in 1918, arguably it only did so in 1998 with the signing of the Good Friday Agreement and the institution of genuine democracy in Northern Ireland. But now it hangs by a thread.

The agreement froze the fragile political situation in a way that ended the violence with a truce and created semi-workable local institutions, the better to end London direct rule. The Republican paramilitaries had finally understood they could not win with violence. But they also realised that democratic methods were more likely to succeed, especially in an era when the unloved British state was coming apart at the seams. For the ideological glue of British Unionism is drying out. The Empire has gone, the monarchy is fit only fit to fill pages in Hello Magazine, and Protestantism has given way to consumerism.

The calculation behind the agreement is that we have a virtual reunion in everything that matters – economy, culture, an open border, shared institutions. That removes the historical incubus for violence. Above all, the Irish – backed up by the EU – have vague but real rights in the North, effectively guaranteeing the safety and status of the Catholic minority. Enough regard is awarded to the increasingly fragmented “Protestant” community to ease them into the new settlement. Given enough time, Ireland will become one entity in practice, if not name.

But Brexit has upset the political apple cart. Brexit means different laws, different trade rules, different medical and food regulations, different investment and funding structures, different commercial systems. It may not happen immediately, but convergence has been replaced with divergence. Worse, all this is happening when Brexit is being driven by English national paranoia and a minority Government in alliance with the most reactionary part of residual Ulster Unionism.

The infamous “backstop” was invented to reassure everyone this inevitable impasse can be avoided. Essentially, it guarantees nothing will change unless somebody comes up with a way of reconciling Brexit with the North staying in the single market and customs union. I have news for you: no such reconciliation is possible unless we scrap Brexit. Say it loud and clear: Brexit and the Good Friday Agreement are incompatible.

Which leaves a limited number of options. The English Brexiteers and the DUP could abandon the agreement. Their narrow Unionist nationalism may favour that route. Given Irish history, we all know where that could lead. Alternatively, Brexit may unwind. But even if it does, the blow to the credibility of the Westminster system can only accelerate the disintegration of the United Kingdom – especially as staying in the EU (aka “betrayal”) will stimulate an English national party in one form or another.

The people of Northern Ireland have one powerful tool at their disposal: under the agreement, they can trigger a border poll which the UK is obliged to respect. The moment they chose to leave the UK, they can. Recent opinion polls show no great rush to demand such a border vote. Nor do they indicate a clear majority for Irish unity. Yet if a border poll took place, I wouldn’t bet on those Catholics currently agnostic on Irish unity voting to defend a Northern Ireland run by the DUP. And if Northern Ireland quits the UK, can Scotland, Wales and even Cornwall be far behind?