The first ministers of Wales, Scotland and Northern Ireland have declared that "Westminster's time is coming to an end", and that the UK government should "prepare" for constitutional change,
BBC reports.
The nationalist leaders from Plaid Cymru, Sinn Féin and the SNP - who want their countries to leave the United Kingdom - signed an agreement on Monday which said no Westminster government had the right to "block democracy".
But while Scotland's John Swinney and Northern Ireland's Michelle O'Neill called for referendums at a joint press conference, Wales' Rhun ap Iorwerth declined to give a timetable for one in his country.
Labour and Reform accused Plaid of wanting to break up the UK.
Ap Iorwerth will hold further talks with Swinney in the afternoon in their roles as government leaders, with both men expected to sign an agreement on "future collaboration in areas of shared interest".
For the first time since devolution began, Wales, Scotland and Northern Ireland all have first ministers who want to leave the United Kingdom.
All three met on Monday as representatives of their parties. Sinn Féin president Mary Lou McDonald also attended.
The memorandum of understanding said: "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.
"No Westminster government has the right to block democracy or undermine the principle that our people will decide their own future.
"We recognise that our parties have different constitutional positions and that each nation will determine its own future in its own way and in its own time."
Plaid has ruled out an independence referendum before the next Senedd election in 2030.
At the press conference, Ap Iorwerth said there was a "growing recognition that Westminster is not working" and "power genuinely needs to be brought closer to people and communities".
"Wales should have the power, the resources, the fair treatment we need as a nation to build the future our people deserve," he said.
SNP leader Swinney said Monday was a "pivotal moment in the constitutional journey of the United Kingdom".
He said the elections last May for each nation created a situation with first ministers who believe "their countries should decide their own future".
"That principle of self-determination in an alienable right," he said.
