Political parties governing Scotland, Wales and Northern Ireland have signed a joint agreement aimed at pursuing separation from the United Kingdom. The leaders of the three regions signed the memorandum of understanding at a meeting in Cardiff, the capital of Wales, on Monday (September 14).

The agreement was signed by Scotland’s First Minister and Scottish National Party (SNP) leader John Swinney, Plaid Cymru leader Rhun ap Iorwerth, and Northern Ireland’s First Minister and Sinn Féin vice president Michelle O’Neill. Sinn Féin president Mary Lou McDonald also signed the agreement.

Although the three regions have their own parliaments, they are not independent or sovereign states.

The agreement states that all three regions have the right to self-determination and that each nation will decide independently, according to its own process and timetable, whether to leave the United Kingdom. It also commits each region to seeking to rejoin the European Union after achieving independence.

Speaking at a joint press conference after the signing, Michelle O’Neill said they were going through a “huge and inevitable change,” adding that no UK prime minister would be able to stop the momentum.

“Westminster has not delivered for our people and never will. We have the right to self-determination, and collectively we want to send that message to Westminster,” she said.

Referring to Sinn Féin’s campaign for Irish reunification, O’Neill said recent remarks by US President Donald Trump demonstrated that the long-standing issue had gained significant support.

Trump recently expressed his desire to see a “united Ireland.” The latest initiative is being seen as an effort to increase political pressure on UK Prime Minister Andy Burnham.

Following Plaid Cymru’s victory in the Welsh election in May, this is the first time that three separatist parties have simultaneously been in power in their respective regions.

Opposition parties, however, have strongly criticised the new alliance. Scottish Conservative Party leader Russell Findlay said most people in Scotland would be angry to see John Swinney join forces with Sinn Féin with the aim of breaking up the United Kingdom.

Harriet Cross, the Conservative shadow Scottish secretary, said Prime Minister Andy Burnham’s recent remarks had handed nationalist leaders new ammunition to push for the breakup of the UK.

A spokesperson for the prime minister, meanwhile, said the United Kingdom was strongest as a united country. The government, the spokesperson said, was more committed to ensuring people’s economic security than engaging in constitutional debates or another referendum.