The First Ministers of Scotland, Wales, and Northern Ireland signed a joint memorandum of understanding on Monday (September 14) to signal their intent of putting their respective nations on the path to referendums towards independence from the United Kingdom. The three nations, along with England, make up the UK.At a summit in the Welsh capital of Cardiff, the three leaders — Wales’ Rhun ap Iorwerth, Scotland’s John Swinney, and Northern Ireland’s Michelle O’Neill — as well as the Republic of Ireland’s leader of the opposition Mary Lou McDonald affirmed in the “Cardiff Agreement” that “the political landscape across these islands is changing”.“For the first time ever, there are First Ministers in Scotland, in Wales and in the North of Ireland who are all committed to independence from the United Kingdom… there could be no clearer sign that Westminster’s time is coming to an end,” the memorandum read. “Our nations have the right to self-determination: No Westminster government has the right to block democracy or undermine the principle that our people will decide their own future.” The Cardiff Agreement came on the back of two recent developments: UK Prime Minister Andy Burnham expressing that referendums for Scotland and Northern Ireland were not on the cards, and US President Donald Trump saying on Saturday (September 12) that he would “love” to see the reunification of Ireland.We explain how the UK came to be in the first place, and what British law has to say about conducting a referendum in its constituent nations.Acts of UnionThe British Isles, a group of over 6,000 islands located in northwestern Europe, comprises the two major islands of Great Britain and Ireland besides several smaller islands. Great Britain consists of three nations — England, Scotland, and Wales — whereas Ireland is made up of the Republic of Ireland and Northern Ireland.The name “Great Britain” assumed significance only in the 18th century, when the kingdoms of England and Scotland were united in 1707 by an Act of Union, becoming the United Kingdom of Great Britain.Story continues below this adAlso in Explained | Trump bats for a ‘unified’ Ireland: What led to its partition?Wales, which is also located on the island of Great Britain, was conquered by the English in the late 1200s, but was legally annexed and made a part of the Kingdom of England only in 1536 through an Act of Union.Meanwhile, the island of Ireland had been under British control since the late 12th century but entered the UK as a political entity only in 1801, following a failed Irish rebellion (1798) and the Acts of Union (1800). Thereafter, the UK came to be officially known as the United Kingdom of Great Britain and Ireland. The United Kingdom comprises England, Scotland, Wales, and Northern Ireland. Photo: Wikimedia CommonsThe name, however, lasted for over a century until 1922, when the majority of Ireland — barring six counties that make up Northern Ireland — gained independence from the British after the Anglo-Irish War (1919-21). With Northern Ireland choosing to remain part of the UK, the latter became the United Kingdom of Great Britain and Northern Ireland.Notably, the three First Ministers signed the joint memorandum not in their capacity as heads of their respective governments but as party representatives: ap Iorwerth as leader of Plaid Cymru, McDonald as president of Sinn Féin and Michelle O’Neill as vice president of Sinn Féin, and Swinney as leader of the Scottish National Party (SNP).Story continues below this adMore in Explained | Ten years after referendum, how Brexit has reshaped UK’s economy and politicsAfter the SNP, which considers Scottish independence its core political plank, came to power with an outright majority in the 2011 Scottish Parliament election, it pushed for a Scottish independence referendum. Through a Section 30 order under the 1998 Scotland Act, powers were transferred to allow the Scottish Parliament to legislate for the referendum.On September 18, 2014, the Scottish independence referendum was conducted with the single-point question “Should Scotland be an independent country?”, with voters having to choose yes or no. The result: 55.3% voted No and 44.7% voted Yes, and Scotland remained with the UK.In 2022, the UK Supreme Court ruled that the Scottish Parliament doesn’t have the power to unilaterally call a second referendum on Scottish independence, with the subject “reserved” for the UK Parliament in Westminster, London. Although SNP’s Swinney said Monday that he wants to hold a second Scottish independence referendum by 2031, the 2022 ruling could pose a major obstacle since major British parliamentary parties such as Labour, Conservatives, and Liberal Democrats remain opposed to it.NewsletterFollow our daily newsletter so you never miss anything important. On Wednesday, we answer readers' questions.SubscribeBoth Wales and Northern Ireland are yet to hold an independence referendum in the traditional sense, but the latter in 1973 conducted a border poll to decide on its constitutional status: whether it should remain part of the UK or join with the Republic of Ireland to create a united Ireland. Irish nationalists, who were in the minority and favoured a united Ireland, boycotted the poll: 98.9% of the votes chose to remain in the UK.Story continues below this adLatest polling reported by The Guardian suggests 47% of Scottish voters would opt for independence in a referendum held tomorrow, along with 36% in Northern Ireland and 32% in Wales. Since the 2014 referendum, support for independence in Scotland has stayed around 45-50%. Data suggests a rise in Wales and Northern Ireland as well.As things stand, the UK Parliament retains exclusive legal authority to hold a referendum in any part of the UK. Only constitutional changes — in the form of the UK Parliament transferring powers to the respective three national parliaments — can facilitate independence referendums, using an order similar to the one granting the Scottish referendum in 2014. This explains why the Cardiff Agreement calls on the British government “to prepare for, plan and facilitate constitutional change in each jurisdiction”.