A United Front Against the Union: Celtic Leaders Prepare Landmark Cardiff Declaration
Scotland, Wales and Northern Ireland’s nationalist leaders will demand democratic routes to self-determination—but the three nations face very different constitutional paths
13 September 2026. The leaders of the governing nationalist parties in Scotland, Wales and Northern Ireland are preparing to meet in Cardiff on Monday, 14 September, for an unprecedented summit that could mark a significant new stage in the debate over the future of the United Kingdom.
Scottish National Party leader John Swinney, Plaid Cymru leader Rhun ap Iorwerth and Sinn Féin vice-president Michelle O’Neill are expected to sign a memorandum of understanding asserting that their nations should have the right to determine their constitutional futures through democratic referendums.
Although all three are First Ministers, reports indicate that they will sign the declaration in their capacities as party leaders rather than as heads of their respective devolved governments. This is an important distinction: the memorandum will represent a coordinated political position, not a legally binding act capable of authorising referendums or dissolving the United Kingdom. Nation.Cymru
A Common Demand—but Three Different Constitutional Journeys
The Cardiff declaration is expected to cover self-determination, economic cooperation, energy, Europe and closer relations among the three nations. Its central message will be that constitutional decisions should ultimately belong to the people of Scotland, Wales and Northern Ireland rather than remain under the exclusive control of Westminster.
The summit is symbolically powerful because, for the first time, the devolved governments of Scotland, Wales and Northern Ireland are led by politicians whose parties support leaving the United Kingdom in its present form.
Yet it would be misleading to suggest that the meeting will immediately “kick-start” the break-up of Britain. Scotland, Wales and Northern Ireland have different political circumstances, levels of public support and legal mechanisms for constitutional change.
Scotland: Independence Support Without the Legal Power to Hold a Vote
Scotland held an independence referendum in 2014 after Westminster temporarily transferred the necessary authority to the Scottish Parliament. Voters chose to remain in the United Kingdom by 55.3 per cent to 44.7 per cent.
The constitutional position was clarified in 2022, when the UK Supreme Court unanimously ruled that the Scottish Parliament could not legislate unilaterally for another independence referendum. The Union and the UK Parliament are reserved matters, meaning that a lawful new vote would require Westminster’s cooperation or a modification of the devolution settlement. UK Supreme Court
The current dispute intensified after Prime Minister Andy Burnham told MPs that another Scottish referendum could become possible if there were a clear and sustained public consensus. John Swinney interpreted the comment as recognition that Scotland must have a democratic route to choose its future. Downing Street subsequently insisted that government policy had not changed, while Burnham told Swinney that another referendum remained off limits.
This contradiction has strengthened the nationalist argument for a permanent and transparent referendum mechanism rather than one dependent upon the political preferences of each UK government.
Wales: A Nationalist Government, but No Majority for Independence
Wales is entering a new constitutional era following Plaid Cymru’s historic Senedd election victory and the appointment of Rhun ap Iorwerth as the country’s first non-Labour First Minister since devolution.
Ap Iorwerth has argued that Wales must be treated as a nation rather than as an English region and has demanded greater powers, including control over policing and justice. However, he has rejected claims that Monday’s meeting is simply a conspiracy to destroy the United Kingdom. He describes his objective as strengthening Wales and allowing its people to determine the country’s eventual destination. The Guardian
Welsh independence nevertheless remains a minority position. A September Survation poll conducted for YesCymru placed support at 32 per cent among likely voters after undecided respondents were excluded, compared with 68 per cent opposed. Support was considerably higher among voters under 45, suggesting that the long-term direction of opinion may differ from the present balance. Nation.Cymru
Like Holyrood, the Senedd does not currently possess the authority to legislate independently for a referendum that would end the Union. Cardiff therefore seeks political recognition of a democratic principle rather than the immediate legal power to declare independence.
Northern Ireland: A Different Legal Settlement
Northern Ireland’s constitutional position is fundamentally different from that of Scotland and Wales.
The Belfast–Good Friday Agreement and the Northern Ireland Act 1998 provide an explicit legal route to Irish reunification. The Secretary of State for Northern Ireland has the power to call a border poll and is legally required to do so if it appears likely that a majority of voters would support Northern Ireland leaving the UK and becoming part of a united Ireland.
Reunification would require majority support in both Northern Ireland and the Republic of Ireland. The legislation does not, however, specify precisely how the Secretary of State must determine whether majority support is likely. House of Commons Library, Northern Ireland Act 1998
Michelle O’Neill and Sinn Féin can therefore argue that the right to make a democratic constitutional choice is already embedded in an international peace agreement. Their demand is not for Westminster to invent a new mechanism, but to respect and prepare for one that already exists.
Trump’s Intervention Adds International Pressure
The Cardiff summit will take place only two days after US President Donald Trump unexpectedly declared during a visit to Dublin that he would welcome a united Ireland and believed reunification would eventually occur.
His comments provoked a rapid response from Downing Street and Northern Ireland’s unionist leaders, who stressed that Northern Ireland’s future must be decided by its people. Trump’s remarks appeared spontaneous and did not constitute an announced change in official US policy, but they gave the constitutional debate immediate international visibility. The Guardian
The timing is politically significant. A debate that Westminster has attempted to contain within separate national contexts is increasingly becoming a connected discussion involving Scotland, Wales, the island of Ireland, Europe and the United States.
Could an Independent Scotland and Wales Rejoin the EU?
European relations are expected to form part of the Cardiff discussions. Both the SNP and Plaid Cymru regard eventual EU membership as central to their visions for independent Scotland and Wales.
Neither country would automatically become an EU member after leaving the United Kingdom. Each would need to negotiate accession, demonstrate compliance with EU law and secure the unanimous approval of existing member states.
Northern Ireland would follow a different route. If it voted to join the Republic of Ireland, it would become part of an existing EU member state rather than seek membership as a newly independent country. This European dimension creates another important distinction among the three constitutional projects.
A Historic Challenge, Not an Immediate Break-Up
The Cardiff memorandum cannot itself create referendums, transfer constitutional authority or end the United Kingdom. Public consent, legislation, negotiations and—in Scotland and Wales—Westminster’s cooperation would still be required.
Its significance is political rather than legal. Three nationalist leaders are coordinating their strategies and challenging the assumption that constitutional questions can be postponed indefinitely by the UK Government.
For unionists, the summit will be seen as a warning that the territorial integrity of the United Kingdom can no longer be taken for granted. For nationalists, it represents an opportunity to establish self-determination as a shared democratic principle while respecting the distinct choices of each nation.
The United Kingdom is not about to disappear after one meeting in Cardiff. But the foundations of the Union are being questioned simultaneously in three of its four nations—and, for the first time, their political leaders are preparing to answer that question together.
Monday’s declaration may not begin the legal break-up of the United Kingdom. It could, however, begin a more coordinated and consequential struggle over who has the right to decide its future.