They certainly can and have also exercised this. The UK was part already in the EU when the Good Friday Agreement was signed. "In March 2017 the Scottish Parli

They certainly can and have also exercised this. The UK was part already in the EU when the Good Friday Agreement was signed. "In March 2017 the Scottish Parliament authorised the Scottish Government to seek to hold a proposed second Scottish independence referendum." https://en.wikipedia.org/wiki/Proposed_second_Scottish_independence_referendum https://en.wikipedia.org/wiki/Proposed_second_Scottish_indep... "The agreement reached was that Northern Ireland was part of the United Kingdom, and would remain so until a majority of the people both of Northern Ireland and of the Republic of Ireland wished otherwise. Should that happen, then the British and Irish governments are under "a binding obligation" to implement that choice." https://en.wikipedia.org/wiki/Good_Friday_Agreement#Status_of_Northern_Ireland https://en.wikipedia.org/wiki/Good_Friday_Agreement#Status_o...