THERE has been much jeering and scoffing at the news that Boris Johnson is persevering with the idea of a Union Bridge between Scotland and Northern Ireland despite the technical challenges.

Ha ha, say nationalists. The way things are going it’ll likely be a bridge between two independent countries.

There is Sinn Fein winning the popular vote in Ireland and demanding a referendum on reunification. And Scotland is to have one next year, according to Nicola Sturgeon.

Well, in your dreams.

There’s unlikely to be a Scottish referendum any time soon. Sinn Fein is in no position to demand a border poll, while it remains a minority in the Irish parliament, the Dail.

It wasn’t only or even mainly Sinn Fein’s policy on a United Ireland that drove leader May Lou McDonald’s success. The campaign focused on housing, health and pensions.

Moreover, not everyone in the Republic is enthusiastic about reuniting with the North. Even some nationalists worry about taking responsibility for the £10 billion or so the UK pumps annually into The Six Counties, as Sinn Fein (SF) calls the province.

Then there’s all the sectarianism and the legacy of the Troubles. Unionist paramilitaries haven’t gone away either. This makes it all the more remarkable that what used to be the political wing of the Irish Republican Army has become a major player in Irish politics. SF was regarded as de facto terrorist itself until recently. The idea it could ever get near forming a governing coalition was regarded as ridiculous.

But after this election, Sinn Fein can no longer be dismissed as a relic of sectarianism. It came top with 24 per cent of the popular vote against 22 per cent for Fianna Dail and 20 per cent for Leo Varadkar’s Fine Gael. Had Mary Lou McDonald fielded more candidates, SF might have won more than its 37 seats in the Dail, one fewer than Fianna Fáil. It was a rare case of a political party actually under-estimating its electoral support.

Seismic is an overused term in politics,but this election really is earthshaking, not least for the future of the UK. Leo Varadkar, the Fine Gael Taoiseach, has been looking suitably shaken.

He insists he will not contemplate any alliance with “extremist” Sinn Feiners, one of whose TDs launched into a rendition of the Irish rebel song “Come out ye Black and Tans” at a Dublin count. Michael Martin of Fianna Fáil isn’t ruling out a coalition but is instinctively hostile.

The establishment parties will do all in their power to lock Sinn Fein out of office during the coming weeks of coalition horse trading. But it seems unlikely they can keep the charismatic Mary Lou in her box.

This is because nationalism is back in a big way in Ireland as in the UK. Yes, the grievances of young people without housing and older folk worried about pensions aren’t intrinsically nationalist. But these grievances are now being expressed by voting for the party of Irish nationalism par excellence.

It is similar to the way many Scottish voters, with similar complaints, turned suddenly to the independence cause in 2014, obliterating Labour in Scotland.

Radical nationalism is now the driving force in modern politics. It is redrawing the political map across Europe as voters turn away from neoliberalism and globalism.

We see it in the Yellow Vest movement in France, in populist parties in Italy and, yes, even in Brexit. That was essentially an English nationalist rebellion against the EU.

The BBC’s former World Affairs Editor, John Simpson, attracted much criticism for tweeting his regret that Ireland had “succumbed to populism”. The implication is that Sinn Fein remain extremist and its success is a bad thing.

Commentators like Simpson used to say much the same about Alex Salmond’s SNP. Many metropolitan intellectuals still regard populism as synonymous with racism and bigotry.

But this equation of nationalist movements with the political right makes little sense. Both the SNP and Sinn Fein triumphed from the left. All nationalisms not the same.

Fianna Fáil and Fine Gael are also nominally nationalist parties, dating from the Irish Civil War. They’re “Soldiers of Destiny” and “Tribe of the Irish” respectively. Sinn Fein, meaning “We Ourselves” actually sounds less militantly nationalist.

In recent years they’ve become identikit centrist parties. Fine Gael is generally considered slightly more right wing and pro big business than Fianna Fáil, which used to represent farmers and small business. But it’s hard to tell. The two old parties are basically rival networks of patronage, cronyism even, with little ideological depth.

Fianna Fáil had the misfortune to be in office during the 2008 financial crash, which hit Ireland hard. The country was traumatised by the weight of debt left by the collapse of the Irish banks.

Fine Gael under its seemingly more progressive Taoiseach, Leo Varadkar, thought it had inherited the upswing. In GDP terms it has. Ireland has one of the highest growth rates in Europe and national income per head is higher than the UK’s.

Mr Varadkar, who is openly gay, won plaudits for legalising abortion and same-sex marriage. But this progressive gloss did not prevent Fine Gael being seen as in the pockets of rampant capitalism.

He won the battle of Brexit too, but lost the war for domestic popularity as young and old turned in disgust from the grotesque inequalities of wealth in Ireland. Brexit was not, by common consent, a significant issue in the election. But it must have played a part, if only subliminally.

The North is to remain in regulatory alignment with the Republic, while Britain erects a border in the Irish Sea. This de facto economic reunification of Ireland has transformed the border question.

It’s no longer a question of Brits out. They’re going. Irish nationalism is no longer about the gun, but about the EU single market. The dream of Irish unity is becoming a reality through the ballot box. Formal unification seems only a matter of time.

The SNP has historically shunned Sinn Fein, fearing guilt by association. That must surely now change. It is now a legitimate democratic force.

But there is a warning here for Nicola Sturgeon. The SNP can’t afford to abandon its left-wing radicalism, or trade it for LGBT and gender politics. If the SNP becomes another party of the establishment it could share the fate of Leo Varadkar.