Swinney, ap Iorwerth and O'Neill sign a Cardiff self-determination text

The first ministers of Scotland, Wales and Northern Ireland sat in Cardiff on Monday and signed a text that said Westminster has no right to block democracy. John Swinney of the Scottish National Party, 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. It was the first time since devolution that all three devolved governments have been headed by parties that want to leave the United Kingdom.

The memorandum states that the nations have the right to self-determination and that no Westminster government has the right to block democracy or undermine the principle that people will decide their own future. It adds that for the first time, people across these islands have first ministers in Scotland, in Wales and in the North of Ireland who are all committed to independence from the United Kingdom. The four leaders wrote that the future of their nations belongs in the European Union and that Westminster's time is coming to an end. They called on the British government to prepare for, plan and facilitate constitutional change in each jurisdiction.

They met as party leaders, not as a formal council of governments. That distinction matters. O'Neill cannot bind Northern Ireland's power-sharing executive to a unity referendum. Ap Iorwerth has ruled out pushing for a Welsh vote now. Swinney wants a Scottish referendum and has no legal path to hold one without London. The document itself records the gap: the parties have different constitutional positions and each nation will determine its own future in its own way and in its own time.

Plaid Cymru won the Senedd election in May. That result completed a set that began when the SNP took Holyrood and Sinn Fein took the largest designation in Stormont. The Cardiff meeting was the first face-to-face session of the three leaderships since that Welsh vote. In the afternoon Swinney and ap Iorwerth signed a separate Cardiff Agreement on joint work: child poverty, the cost of living, international engagement, energy and the protection of self-government. The text says Scotland and Wales are on different constitutional journeys but share trust in their people's ability to decide their future for themselves.

The political use of the day is obvious. Nationalist parties want a photograph and a shared line before the next UK budget and before any new argument over a second Scottish vote. The legal use is thinner. The Supreme Court has already held that Holyrood cannot legislate a referendum that would affect the Union. Northern Ireland's Good Friday arrangements set tests for a border poll that sit with the Secretary of State, not with Stormont. Wales has no statute that even sketches an independence vote. A memorandum does not change those rules.

What it does change is the coordination cost. The three parties now have a written baseline on Europe, on the claim that London cannot veto a democratic choice, and on practical files such as energy and poverty where they can act inside existing powers. If they keep that channel open, Downing Street will face three governments speaking from one sheet on those files rather than three separate briefs.

McDonald's presence tied the meeting to Irish parliamentary politics as well as to Belfast. Sinn Fein wants a unity referendum on a timetable it does not control. Standing in Cardiff with Swinney and ap Iorwerth lets the party show a wider frame without waiting for the Northern Ireland Office. For Plaid, the value is recognition after a first win of the Senedd. For the SNP, the value is company after years of asking London for a vote and being refused.

None of the four leaders named a date. The next test is whether the Cardiff Agreement produces joint papers that civil servants in Edinburgh and Cardiff actually use, and whether O'Neill can repeat the language inside a five-party executive that includes unionists. Until that happens, Monday is a statement of intent with a precise sentence at its centre: London, they say, does not hold a veto over the question itself. Westminster has not accepted that sentence. The argument now has a signed text to quote.