Celtic first ministers tell Westminster it has no right to block self-determination

The first ministers of Scotland, Wales and Northern Ireland stood in Cardiff on Monday and signed a text that said Westminster has no right to block their nations from choosing a future outside the United Kingdom. John Swinney of the SNP, Rhun ap Iorwerth of Plaid Cymru and Michelle O'Neill of Sinn Fein were joined by Sinn Fein president Mary Lou McDonald, who leads the opposition in the Irish Dail.

The memorandum said it was the first time people across these islands have first ministers in Scotland, Wales and the North of Ireland who are all committed to independence from the United Kingdom. It added that momentum is behind the movements and that constitutional change is coming. The four called on the British government to prepare for, plan and facilitate that change in each jurisdiction.

They met as party leaders rather than as a formal meeting of governments. In the afternoon Swinney and ap Iorwerth signed a separate Cardiff Agreement on joint work covering child poverty, the cost of living and international engagement.

What the text actually binds

The document is careful on method. It says each nation will determine its own future in its own way and in its own time. Swinney and O'Neill speak openly about referendums. Ap Iorwerth, whose party won the Senedd election in May, has ruled out pushing for a Welsh vote now. That difference is written into the text rather than papered over.

The future of our nations belongs in the European Union, the memorandum said. For people watching across these islands, and for people watching around the world, there could be no clearer sign that Westminster's time is coming to an end. The line is political theatre. It is also a statement of preferred end-state: exit from the UK paired with a return to the EU, which Scotland voted to remain in during the 2016 referendum and which Northern Ireland already treats through the Windsor Framework.

Andy Burnham, the new prime minister, has said he will not engage in constitutional debates or further referendums after appearing last week to leave a door ajar on a second Scottish vote. Mary Lou McDonald's reply, reported by the Telegraph, was that Burnham cannot stop the end of the United Kingdom.

Why Cardiff, and why now

Plaid Cymru's win in May completed a set that devolution has not seen before. Scotland has had SNP-led government for years. Northern Ireland's power-sharing rules put Sinn Fein in the first minister's office once it became the largest party. Wales had been the holdout. With ap Iorwerth in the Senedd, the three Celtic executives now share a constitutional goal even as they share almost no identical path to it.

Northern Ireland's case is governed by the Good Friday Agreement. A border poll is a Secretary of State decision, triggered if it appears likely that a majority would vote for a united Ireland. Scotland's 2014 referendum was a one-off deal with Westminster. The UK Supreme Court later held that Holyrood cannot legislate a second vote on its own. Wales has never had an independence referendum and has weaker polling for one.

Those legal facts sit under the rhetoric. A memorandum cannot force a poll. It can coordinate talking points, share civil-service contacts on energy and trade, and make it costlier for a new prime minister to treat the three files as separate nuisances.

Burnham's early mark has been consumer law, including an accelerated ban on subscription traps from January 2027, and a refusal to reopen the constitution. The Cardiff text is designed to deny him that quiet. It puts three first ministers and the likely next Irish prime minister on one page saying the union's time is up. The next move is his, or it is a long wait for votes that none of the signatories can call by themselves.