In four weeks, the shape of British politics is likely to change dramatically.For the first time, nationalists who aspire to break up the UK are expected to be in control of Scotland, Wales and Northern Ireland simultaneously.“The change will be seismic,” said Angus Robertson, a senior minister in the Scottish government.Opinion polls consistently suggest that after the elections on 7 May, England will be flanked by countries run by restless centre-left nationalist parties – Plaid Cymru in Cardiff, the Scottish National party in Edinburgh and, in Belfast, Sinn Féin, which shares power with the Democratic Unionists.That raises the prospect of significant constitutional disputes that would thrust Keir Starmer’s Labour government in London – or, if he is ousted after May’s elections, that of his successor as prime minister – into very difficult waters.

Sources say all three parties are in talks about combining forces to challenge the UK government on areas such as spending, taxation, welfare and rejoining the EU.Meanwhile, Starmer will probably be wrestling with more English local authorities run by Reform UK, standard bearer for its form of British nationalism.The disputes could erupt into open conflict if the SNP wins an overall majority in May and uses that to demand a second independence referendum, potentially as soon as 2028 – a prospect some polls suggest is realistic, but which is still seen as unlikely due to Holyrood’s proportional voting system.“It’s really important to appreciate that if we are in a situation with three nationalist first ministers out of four nations of the UK, the status quo is not sustainable,” Robertson told the Guardian.“There is going to have to be a massive step change in how the UK deals with the other nations of the United Kingdom.

”After decades of collaboration between Plaid Cymru and the SNP at Westminster, Scottish ministers have recently helped prepare Plaid for government in Cardiff, sharing a playbook of tactics and experience garnered after 19 years in control in Edinburgh.Rhun ap Iorwerth, the Plaid Cymru leader who aspires to end 103 years of Labour domination in Wales, is preparing to demand that Starmer give Wales powers long enjoyed in Scotland, such as devolved policing and justice, control over its seabed and increases in funding.“The Labour party became so preoccupied with holding on to power that it forgot where it came from and who it was there to serve,” ap Iorwerth told delegates at Plaid Cymru’s autumn conference.“We don’t have to believe Westminster when they tell Wales ‘this is your lot’ and that we should be ever grateful for what we’re given.We can do things differently.

[We] are not here to repair Labour.We are here to replace them.”In a further sign of the UK’s shifting constitutional politics, Scotland’s first minister, John Swinney, has tentatively allied himself with Sinn Féin’s deputy leader, Michelle O’Neill, the first minister of Northern Ireland’s power-sharing government – an alignment that was previously politically unthinkable.Pictured together last year at the funeral of Pope Francis at the Vatican, O’Neill backed calls from Swinney in mid-March for an emergency summit to discuss the energy crisis amid the Iran war, with the pair meeting at government summits.There are expectations too that Sinn Féin would use Plaid Cymru and SNP victories next month to boost its demands for a poll on Irish reunification by 2030, making that central to its Northern Irish election campaign in May 2027.

One senior Labour source has heard centrist politicians in Northern Ireland predict that if Nigel Farage and Reform win the next UK election, it would sharply increase support for a border poll and reunification, including in their ranks,Those prospects have unnerved some of the UK’s western allies,Some diplomats fret that renewed constitutional conflict within the UK could further weaken Starmer’s government at a time of immense global instability,Other diplomats are more sanguine about the risks to the UK’s stability, as are experts on British constitutional politics,Michael Keating, an emeritus and honorary professor with Aberdeen and Edinburgh universities, argued nationalist victories would present the UK Labour government with a significant test of its maturity rather than immediately threaten the UK’s territorial integrity.

In other countries, nationalist parties run regional governments without existentially threatening central governments.In Canada nationalist parties have run Quebec, and in Spain nationalist parties in Catalonia and Basque Country cooperate with socialist and conservative governments in Madrid.“It’s high temperature in Spain, but they know what the rules are and they make it work,” Keating said.“[This] is normalising devolution; normalising the plurinational state.This is a democratic form of politics.

”He argued Brexit had made the long-running conflict between Whitehall’s desire to assert its sovereignty by enforcing central control and the growing pressure for greater local autonomy in Scotland and Wales after 27 years of devolution even more significant.When Britain was in the European Union, each part of the UK followed the same EU rules, but since Brexit Whitehall has assumed ultimate control over the devolved nations, much to their chagrin.Starmer came to power in 2024 pledging to heal the deep divisions that marred relations between the Scottish, Welsh and UK governments under the Tories, and to respect the UK’s nations and regions.For many months that closer working relationship with Scotland largely endured but under the current Scottish secretary, Douglas Alexander, who is widely regarded as a hawk when it comes to protecting Westminster’s interests, relations have soured markedly.In March, ap Iorwerth brandished a leaked UK cabinet memo in the Senedd in which Starmer implicitly acknowledged Labour could lose in Scotland and Wales but said the UK should still avoid being “overly deferential” to devolved governments.

Starmer said in it: “Each of us will maintain a professional and respectful working relationship with our counterparts in devolved governments.” But he added: “We should be confident in our ability to deliver directly in those nations, including through direct spending, even when devolved governments may oppose this.”Eluned Morgan, Wales’s Labour first minister, has voiced frustration at Labour policy in Westminster, including the attempts to cut winter fuel payments and disability benefits.Her colleagues are also furious Starmer’s government has failed to honour manifesto commitments in 2024 to devolve youth justice and probation, and used the post-Brexit internal markets act to impose UK spending on town centre modernisation in Wales, accusing the prime minister of rolling back devolution.One senior Labour source said: “Certainly, two years into that administration, there is next to nothing to show on issues which matter to Welsh Labour.

”Laura McAllister, a professor of public policy at Cardiff University, said that even so, there was no certainty that collaboration between the three parties at UK level would run smoothly or that Plaid Cymru, the SNP or Sinn Féin would enjoy success domestically.A Plaid Cymru victory in May would be “a pretty revolutionary change” for Wales, she said, but the party would first have to prove it could govern better than Labour: since devolution began in 1999, NHS and education standards in Wales have dropped below the other UK nations, and poverty has deepened.Swinney, if he wins in May, has to wrestle with a £5bn spending shortfall; the SNP has retained power by deploying expensive policies it has failed to properly budget for, and public confidence in public services is consistently lower than the 35% support the SNP enjoys in opinion polls.Both parties will also be running minority governments and will be heavily dependent on deals with other parties with their own demands.Sinn Féin’s power-sharing government with the DUP is also extremely fractious, and public confidence in Stormont and Northern Ireland’s ailing public services is souring.

There is no certainty their partnership will survive to next year’s election, or that Sinn Féin’s vote will increase.McAllister said Plaid Cymru and the SNP were at odds over some key areas of policy, particularly reforming the Barnett formula, the Treasury system that funds the UK’s nations and regions.Plaid Cymru has long argued Barnett unfairly penalises Wales, which has the lowest funding per head of the three devolved governments, but the SNP will bitterly resist any changes that cut Scottish spending.“[Ap Iorwerth] knows his first term has to be about showing they can govern effectively, like the SNP did.In Scotland, the terrain and conversation has moved on drastically” due to the SNP’s electoral successes, McAllister said.

Scottish Labour sources were reluctant to speculate about the challenges posed by nationalist governments across the three devolved nations,Party leaders insist Labour could yet form the next Holyrood government, if the post-election arithmetic works,But a Scotland Office source said UK ministers would constantly prioritise cooperation,“Over the 25 years of devolution, the Scotland Office has, at different stages, been led by different parties and so too has the Scottish government,That is in the very nature of democracy,” they said.

“Whatever the outcome of the election in May – in which not a single vote has yet been cast – the UK government, as it has previously, will continue to engage constructively with the Scottish government to advance the best interests of Scotland within the United Kingdom.”