For the First Time, Scotland, Wales and Northern Ireland All Have First Ministers Who Want Out of the U.K. On Monday Their Parties Signed a Pact in Cardiff Declaring 'Westminster's Time Is Coming to an End.'

The leaders of the largest pro-independence parties in Scotland, Wales and Northern Ireland met in Cardiff on Monday and signed a joint memorandum asserting their nations' "right to self-determination," a rare coordinated challenge to London from three governments that, for the first time, are all led by people who want to leave the United Kingdom.

John Swinney of the Scottish National Party, Rhun ap Iorwerth of Plaid Cymru and Michelle O'Neill of Sinn Féin, each of whom serves as first minister of their respective nation, attended in their capacity as party leaders rather than heads of government. Sinn Féin president Mary Lou McDonald also took part.

"Our nations have the right to self-determination," the memorandum states. "No Westminster government has the right to block democracy or undermine the principle that our people will decide their own future." It continues: "For the first time ever, 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 document goes further than a statement of principle. It calls on the British government to "prepare, plan and facilitate constitutional change in Wales, Scotland and the north of Ireland," declares that "the future of our nations belongs in the European Union," and commits the three parties to "identifying practical areas of partnership around the economy, energy and European and international cooperation." Its most pointed line is aimed at a global audience: "For people watching across these islands, for people watching around the world, there could be no clearer sign that Westminster's time is coming to an end."

The three parties do not agree on how or when to get there. The SNP wants a second referendum after Scotland voted 55 percent to 45 percent to stay in the U.K. in 2014. Sinn Féin wants Northern Ireland to join a united Ireland, and under the 1998 Good Friday Agreement the British government must call a border poll if the Northern Ireland secretary judges that a majority would likely vote for unification. Plaid Cymru, which Laura McAllister of Cardiff University noted "was elected with heavy emphasis on avoiding the issue of independence," has no plan for an early vote. None of the three nations has a legal path to leave the U.K. on its own.

Prime Minister Andy Burnham has already said no. On Aug. 27, the newly elected Labour leader said a referendum on Northern Ireland leaving the U.K. was "off the table," and he has described a second Scottish vote as "off limits," though he later said one remained possible with "clear consensus." The Cardiff meeting also followed comments from President Trump, who told reporters during a visit to Ireland on Saturday that a united Ireland would be "fantastic." "Now the UK will have something to say about it," Trump said, "but I think it would be a great thing." Burnham responded that his position on Irish unification was unchanged.

Polling shows real but uneven support for leaving. A Survation survey found 47 percent of Scots back independence. A University of Liverpool poll found 36 percent in Northern Ireland would vote for reunification. In Wales, Survation put support for independence at 32 percent.

McAllister said the agreement's wording was "deliberately" cast in "the broader constitutional language of self-determination," and called the meeting "very tactical and very strategic." "This is the first time that the nations of the United Kingdom are attempting to drive the constitutional question," she said. Whether they can drive it anywhere depends on a government in London that has, so far, refused to move.