If the British state is under the impression that the SNP’s crisis has stalled the movement to break up the UK, then it’s not paying attention to what’s happening across the Irish Sea. When Sinn Féin wins the next general election in the Republic – which polls say it almost certainly will – it will have two items on its to-do list.

1. Tame Irish capitalism. 2) Unite Ireland.

The need for the former is driving the party’s popularity. The latter will panic the British state. For the first time in modern history, the UK will have on its border a government intent on breaking it up. The SNP runs Scotland from within a constitutional system controlled by Westminster and without international representation. Sinn Féin will have no such restrictions.

Even the fact of the party’s victory will be extraordinary, likely triggering a screech of Anglo-British nationalism.

And Sinn Féin leading the Republic of Ireland will likely coincide with Sinn Féin leading Northern Ireland. If the Northern Irish Assembly has reconvened by then, the party’s leader will be the taoiseach in the south, and its deputy leader the first minister in the north – in a sense, a form of de-facto unity.

“You just have to say it out loud” to begin to see the implications, says Colin Harvey, a law professor at Queen’s University in Belfast and a board member of Ireland’s Future, a non-profit that campaigns for unification. “You increasingly hear people talk about a referendum [on Irish unity] happening this decade.”

In the Republic

For a hundred years, Sinn Féin in the Republic of Ireland was a historical curiosity. Both of Ireland’s traditional main parties, Fianna Fáil and Fine Gael, emerged as splits from it during the civil war of the 1920s, but since then, the parent party itself has barely registered, its political support inhibited by its association with the IRA.

In the 1997 Irish general election, Sinn Féin got 2.5% of the vote share – the party’s best result since 1961. In 2016, it breached 10% for the first time in 90 years. In 2020, led by Mary Lou McDonald, it came first in the popular vote, with 25%, but she was excluded from power by an alliance between Fianna Fáil and Fine Gael. Since then, her party’s support has surged above 30% in the polls, consistently leading its rivals by more than 10%. The next election is due by January 2025, and it’s extremely likely that McDonald will become taoiseach.

The party’s growth is largely because it is left-wing. As property prices have surged back since the 2008 crash, younger people have been pushed out of the housing market. Homelessness rates are rising. And Ireland still doesn’t have proper universal healthcare, despite long-standing promises from all parties. In the 2020 elections, voters listed healthcare and housing as their most important issues, followed by ‘the economy’ and climate change. Reunification of Ireland didn’t feature.

The opening section of Sinn Féin’s manifesto that year was clear: “Sinn Féin is a United Ireland party. Our core political objective is to achieve Irish Unity.” But the party largely won over millennial and Gen Z voters by promising “the biggest council-led house-building programme this state has ever seen”, rent rebates, mortgage caps and, crucially, an ‘Irish NHS’.

Most citizens of the Republic are in favour of a united Ireland, but it’s not a priority – for now. Just as progressive Scottish voters in 2007 and 2011 backed the SNP primarily to oppose Labour’s rightward drift but came to embrace the constitutional consequences of doing so, so Sinn Féin’s new voters in Ireland aren’t supporting them in order to create a constitutional crisis in Britain. That’s just going to be an added bonus.

Northern Ireland

In the North, The Good Friday Agreement is a beached whale: magnificent, stuck, probably dying. It achieved its main aim. The civil war ended. The peace may be incomplete, but it’s held firm. Civil war is unlikely to return.

But the era of Northern Irish politics that began with that peace deal 25 years ago has come to an end. The institutions it created – the Assembly and the Northern Irish executive, the North/South ministerial council – have mostly been suspended for the past five years.

Political Protestants, who traditionally identify as British and are used to dominating, already had difficulty swallowing a settlement that left them the first among equals, the biggest minority in a power-sharing arrangement. Now they’ve been relegated to second place behind the cultural Catholics – who normally think of themselves as Irish – both in raw numbers, according to the 2021 census, and politically, in the form of Sinn Féin election victories. The result is that the political protestants’ largest party, the DUP, won’t even sit at the table.

The local elections in May brought the most extraordinary sign of change. While Unionists could put Sinn Féin’s Assembly success last year down to a three-way split in their own vote, this time, the combined vote for nationalist parties was bigger than the unionists’. Sinn Féin won its first councillors deep in Loyalist country.

Mostly, this success has come from winning over culturally Catholic women. Polling in 2019 showed men were around 10% more likely to vote for Sinn Féin – perhaps because women were put off by the party’s macho image and association with historic paramilitary violence. But while male support has stayed steady since then, female support has shot up over the last year, to the point that women are now around 10% more likely than men to back the party.

But there seems to be something more subtle going on, too. Much of the unionist demise has come from falling turnout among Protestants. For years now, unionist voters I have interviewed have been angry at the DUP over a string of corruption allegations, its failure to stand up to austerity and, for some, its conservative social policies. But they would still show up and vote for them out of fear of a Sinn Féin victory. Now they aren’t bothering.

So while Sinn Féin leader in the north Michelle O’Neill’s efforts to cosy up to unionist communities – attending the coronation, for example – hasn’t persuaded them to vote for her, it seems to have made it harder for the DUP to scare them into turning out to vote against her.

There are other factors making Irish unity look more appealing, too. With the DUP refusing to allow Northern Ireland’s government to form under a Sinn Féin first minister, the Conservative Northern Irish secretary in Westminster has taken control of finances, setting what many are calling a ‘punishment budget’. As one contact – whose job in Northern Irish politics means they must stay anonymous – put it: “While that won’t motivate [DUP leader Jeffrey Donaldson] back into power, it will move us closer to multi-service collapse”.

Thanks to staff shortages, an additional 200 special educational needs classes are needed in Northern Ireland by September to meet demand. Better pay and conditions for doctors means NHS Northern Ireland is facing an exodus of staff to the Republic. Even before the pandemic, Northern Irish patients were around 3,000 times more likely to wait more than a year to see a consultant than those in England. In March this year, the BMA warned that Northern Ireland’s health service is collapsing.

Across the border, the situation looks different.

Ireland is engulfed in a housing crisis, but its homelessness rates are far lower than the UK’s, with five times fewer people experiencing homelessness than in Northern Ireland, despite it having almost three times the population. England’s homelessness rate is also more than twice Ireland’s. In Ireland, the housing crisis is driven by the fact that the average house price has risen to around five times the average wage; in the UK, it’s seven times.

In the UK, 3.6 babies in every 1,000 live births die within the first year of life; in Ireland, it’s 2.6. The average Irish person now lives more than two years longer than the average British person and has had nearly three more years of education.

And while both the UK and Ireland have dangerously unfettered capitalisms, Ireland’s is much more successful. Its raw GDP per capita is more than twice the UK’s. (Though to be fair, Ireland’s figure is puffed up by multinationals registering there for tax reasons, while British equivalents are often in its overseas territories, so not its figure. Per capita Gross National Income figures strip out that fluff, and leave Ireland just 50% richer than the UK.) Average wages are about the same, but Ireland is significantly more equal, with better welfare support.

“It is,” as Brendan O’Leary, a professor at the University of Pennsylvania, says to me, “much, much better to be poor in the Republic of Ireland than it is to be poor in the United Kingdom.”

And the capsize of the Catholic Church in the 2010s in the wake of a string of scandals, followed by the magnificent referendums on abortion rights and marriage equality, has meant Ireland started appearing less and less like a bigoted backwater. In 1991, 92% of Irish people identified as Catholic. By 2011, it was 84%. In 2016, 79%. By 2022, 69%. Its influence has fallen even further. Homosexuality was illegal in Ireland until 1993. Now, the country has a gay Taoiseach.

In Northern Ireland, the result of all this has been a remarkable change in attitudes towards a United Ireland.

In June 2013, just 3.8% of people in Northern Ireland told pollsters they’d vote for a United Ireland ‘now’. Interviewing people across Belfast around that time, huge numbers told me that, though they thought of themselves as Irish nationalists, they would actually vote against unification to keep the NHS and Britain’s welfare state. That was before Brexit and a decade of austerity.

More recent polls tend to show support for unity between 30% and 40%, with around 50% opposing and the rest undecided.

Shifting demographics

The Good Friday Agreement requires the British secretary of state for Northern Ireland to call a referendum “if it appears likely” that most people would back a United Ireland. For those who support reunification, there is still work to do to pass that hurdle – particularly in reaching the two groups that seem open to the idea.

The first is those O’Leary, who leads research into public opinion for the ARINS programme (Analysing and Researching Ireland North and South), describes as the “wobblies” – that is, those who tell researchers that they’ve changed their mind on the question more than once. These people are largely older cultural Catholics, he says. “They’d want to see the model that was specifically on offer. They're probably more concerned about the potentially unsettling effects of unification on their welfare and their lifestyle.”

The second is voters – often young people – who aren’t cultural Catholics but who don’t oppose Irish unification as a principled matter of identity. “There is a significant portion of the Protestant population, at least 7%, maybe a little higher, who favour Irish unification,” he says – a phenomenon that barely existed a decade ago. It could also include those whose backgrounds are mixed or those whose identities lie outside Northern Ireland’s traditional dichotomy. In 2001, 0.4% of people saw themselves as neither Catholic nor Protestant. Now, that’s 20%. Around 7% don’t identify as British, Irish or Northern Irish, but ‘other’, including more than 50,000 people with Eastern European identities.

As my anonymous contact puts it, many of these people are “‘Sunday brunch types’ – remain voting, pro-LGBT, hate the DUP”. They see themselves less as British or Irish, and more as cosmopolitan. They aren’t yet excited by the idea of a United Ireland. But they are open to being. They are a very similar demographic to the one Sinn Féin has won over in droves in the Republic. They are a very similar group to that which has shifted towards supporting Scottish independence over the last decade.

For Harvey, “it’s about breaking down some of the myths” about the Republic, hangovers from its past as an impoverished outpost of the Vatican. “Ireland is a successful EU state. At the end of the day, it’s a proposition about a fairer future for everyone in an Ireland that’s been held back by partition and division,” he argues.

To do this, Ireland’s Future has been calling for the Irish government to do more, including all Ireland civic assemblies looking at key questions for what unification would look like.

There needs to be, Harvey argues, “a much more focussed governmental effort around doing the work in advance – nobody wants to see a repeat of the Brexit mess where people did not really know what they were voting for or against.”

O’Leary argues that “that requires hard work over the rest of this decade” including forming a Ministry of National Reunification and “a standing constitutional forum”.

These things seem much more likely if Sinn Féin wins.

Obstacles to reunification

Another contact – a Northern Irish political strategist – is more sceptical. “I still think a United Korea will happen before a United Ireland,” they say. “There won’t be a United Ireland until Ireland has socialised healthcare.”

And for all its promises to bring social democracy to the Republic, they argue, Sinn Féin has been in government in the North for years and consistently failed to deliver almost anything.

“They had the housing minister, and they haven’t even ended the right to buy!” says my contact, referring to the Thatcher-era policy of allowing tenants to buy the council houses they live in, which has led to a disastrous reduction of social housing stock, and which both Scottish and Welsh governments have stopped.

In the end, whether or not we see a United Ireland likely comes down to two key factors.

Firstly, Sinn Féin's attitude after it wins in the Republic. The party can’t disappoint its young voters – it needs, probably more than anything else, to make good on its promise to build an Irish NHS. It also needs to resolve Ireland’s housing crisis – which will, as O’Leary says to me – require a confrontation with the country’s fear of dense housing and modern urban planning.

And secondly, whether Northern Irish civil society groups and pluralistic social movements can convince their fellow citizens that a United Ireland offers a clearer path to social justice and a better life than the British state. Realistically, this is who would be delivering Irish unity because Sinn Féin probably won’t win over the remaining swing voters in Northern Ireland. The party may look like a fresh force in the Republic, but there are still too many who don’t trust them in the North.

But there is a third factor, too. With more and more Northern Irish voters consciously choosing between a future under London or Dublin rule, it’s not just the Irish state that needs to sort itself out.

Anglo-British nationalism continues to spiral out of control. For the last few years, the British state has at least been able to pretend that a Labour government might come over the horizon, and solve some of the problems created by the Tories and their austerity.

If and when that cavalry does arrive, it will likely come in the flaccid form of Keir Starmer, triangulating towards a far-right Tory opposition. A Sinn Féin-run Ireland may not have to work too hard to convince voters that they are better off under its wings.

On 18 November, openDemocracy is co-hosting a conference on the end of the Union. Speakers from across these islands – Caroline Lucas, Fintan O’Toole, Kojo Koram, Neal Ascherson, Leanne Wood and more – will be gathering with hundreds of people in Edinburgh’s Assembly Rooms to discuss ‘The Break Up of Britain?’. Book your tickets now.