Political leaders from Scotland, Wales, and Northern Ireland have called for significant constitutional changes, suggesting that Andy Burnham could be the "last prime minister of the United Kingdom." The Scottish National Party (SNP), Plaid Cymru, and Sinn Fein formalised their stance in a memorandum signed in Cardiff on Monday, asserting their collective right to determine their own futures.

Sinn Fein president Mary Lou McDonald described the agreement as a historic moment, expressing that the three nations possess an inalienable right to self-determination and will not tolerate interference from the UK government. She highlighted a sense of optimism particularly among younger generations in Scotland, Wales, and Northern Ireland regarding potential independence or unification.

The leaders argued that, under international law, each nation has the right to decide its constitutional status without external coercion. They converged on economic strategies, including rejecting what they called "Whitehall’s broken economic model," focusing on economic growth, energy resource management, and a shared goal of rejoining the European Union.

Westminster maintains that any referendum on independence or constitutional change must be approved by the UK government. This position was reinforced by a UK Supreme Court ruling four years ago stating that Scotland cannot unilaterally hold a referendum without consent from London. Nonetheless, the devolved governments have increased pressure on the central government to facilitate referendums.

SNP Deputy First Minister John Swinney, Plaid Cymru leader Rhun ap Iorwerth, and Sinn Fein vice-president Michelle O’Neill jointly urged Westminster to prepare for constitutional change in their respective nations. They criticized the UK government's current approach as inadequate and out of sync with the aspirations of their populations.

The Cardiff agreement emphasizes that each nation should determine its future through democratic processes reflecting the will of its people. Swinney called for a new Scottish independence referendum within the current parliamentary term, which extends to 2031. He referenced polling data suggesting that a majority of Scots might now favour independence, contrasting with the 2014 referendum result where 55% voted against leaving the UK.

McDonald stated the inevitability of future constitutional votes and described the current political landscape as unprecedented, with all three devolved governments led by nationalist parties. Rhun ap Iorwerth welcomed the collaboration, viewing it as a response to recent electoral shifts in Wales and a rejection of the Westminster model.

In response, Downing Street indicated the UK government’s focus remains on addressing economic challenges such as the cost-of-living crisis and enhancing economic stability. A spokesperson reiterated Prime Minister Burnham’s commitment to strengthening the United Kingdom, emphasizing unity and cooperative problem-solving over division and constitutional debate.