Leaders of nationalist parties in Scotland, Wales and Northern Ireland signed a memorandum of understanding Monday in Cardiff calling on the British government to prepare for potential constitutional changes and allow each nation to determine its own future.

The agreement was signed by Scottish First Minister John Swinney of the Scottish National Party, Welsh First Minister Rhun ap Iorwerth of Plaid Cymru and Northern Ireland First Minister Michelle O’Neill of Sinn Féin. Sinn Féin President Mary Lou McDonald also participated in the meeting.

The memorandum states that the political landscape across the British Isles is changing and calls on the UK government to “prepare, plan and facilitate constitutional change” in Scotland, Wales and Northern Ireland.

The leaders also discussed cooperation involving the economy, energy, international affairs and relations with Europe. The Scottish and Welsh governments separately signed the Cardiff Agreement on Monday, which includes cooperation on international engagement with the European Union.

The independence pact comes as constitutional issues have returned to the center of British politics following Brexit. Scotland voted against independence by 55% to 45% in its 2014 referendum, while Northern Ireland has a separate constitutional framework under the 1998 Good Friday Agreement that provides for a referendum on Irish unity under specified circumstances.

The UK government has rejected calls for an immediate new Scottish independence referendum. Prime Minister Andy Burnham has also emphasized devolution while maintaining that another Scottish referendum is not currently on the government's agenda.

The three nationalist movements do not share identical timelines or constitutional arrangements. The SNP has pushed for another Scottish independence vote, while Plaid Cymru has taken a longer-term approach in Wales. In Northern Ireland, Sinn Féin continues to advocate for Irish reunification.

The Cardiff meeting represents the first coordinated gathering of the three nationalist parties at this level and gives them a common platform on self-determination, even as any changes to the United Kingdom's constitutional structure would require separate legal and political processes in each nation.