Ireland was not British territory from time immemorial, but its relationship with England and later Britain is long and complicated. Before the Middle Ages, Ireland had its own Gaelic kingdoms and local lordships. English royal power began to intervene from the 12th century, followed by centuries of control, colonisation and assimilation, but that control did not cover the whole island from the start, nor was it a modern national union. In 1541, Ireland became a kingdom under the same monarch as England. Only after the Act of Union took effect in 1801 did Ireland formally merge with Great Britain as part of the United Kingdom. In 1922, the Irish Free State was created and most of the island left the UK. Only the 6 north-eastern counties remained inside the UK, becoming today’s Northern Ireland. The point is not that Ireland naturally belonged to Britain, but that centuries of British involvement turned Ireland into a question of state borders.
This also explains why Northern Ireland’s political vocabulary can be confusing. Unionist means someone who supports Northern Ireland remaining in union with the United Kingdom. It does not mean supporting the unification of Ireland. By contrast, Nationalist or Republican usually means someone who favours Irish unity, or a United Ireland. A United Ireland means Northern Ireland leaving the UK and joining the Republic of Ireland in a single Irish state. There have been advocates of Northern Irish independence, sometimes described as Ulster nationalism, but this has always been a fringe position and has never become the formal policy of a major Northern Ireland party. In practice, Northern Ireland’s constitutional choice is binary: remain in the UK, or move towards Irish unity.
Northern Ireland is the product of this unfinished border question. It is not an ordinary devolved region, nor simply a local administrative unit like an English county. It exists because, at the time of Irish independence, the north-east of the island had a large Protestant, pro-British and pro-Union population whose political, religious, landowning and industrial interests were more deeply tied to Britain. Partition assumed that Northern Ireland would have a stable Protestant pro-Union majority. It did not solve the Irish question. It narrowed and concentrated it inside a smaller constitutional container. For the past century, the central question in Northern Ireland has not been tax, transport or local services, but whether the territory should remain in the UK or become part of a United Ireland.
That constitutional divide has long overlapped with religious community. Protestants in Northern Ireland have tended to support unionism and remaining in the UK. Catholics have tended to support nationalism or republicanism and Irish unity. This does not mean every person’s politics is automatically determined by religion. It means housing, schooling, neighbourhoods, parties, marching traditions and historical memory have long been organised along religious lines. In Northern Ireland, Protestant and Catholic identity is not merely about worship. It has also acted as a social marker of national belonging, community security and inherited grievance.
The Troubles, which began in the late 1960s and lasted for 30 years, endured because the dispute was not simply about policy. On the surface, the conflict involved civil rights, policing, housing, employment and electoral arrangements. Beneath it lay a deeper institutional contradiction: one place contained two national imaginations. Unionists saw Britain as a source of security. Nationalists saw British rule as a continuation of historical domination. The importance of the 1998 Good Friday Agreement was not only that it helped end violence, but that it turned this conflict into a managed constitutional framework. It recognised that people in Northern Ireland could identify as British, Irish, or both. It also established the principle of consent: Northern Ireland’s constitutional status can change only with the will of its people.
This makes Northern Ireland constitutionally different from the rest of the UK. The British constitution generally avoids writing down clear routes to secession, because the UK has long relied on parliamentary sovereignty, political convention and useful ambiguity. Northern Ireland is different. Under the Northern Ireland Act 1998 and the wider settlement, Northern Ireland remains in the UK unless a majority votes to join a United Ireland. If the Secretary of State for Northern Ireland believes that such a majority is likely, a border poll can be called. There is still political judgement involved, because the threshold for judging that a majority is likely is not mechanical. But the legal doorway already exists. Scotland, by contrast, still faces a constitutional argument over whether Westminster will authorise another independence referendum. Northern Ireland’s route out of the UK is not an external challenge to the system. It is written into the peace settlement itself.
Demography has weakened the original assumption behind Northern Ireland’s settlement. The 2021 census showed that, for the first time since Northern Ireland was created, people from a Catholic or Catholic-background population outnumbered those from a Protestant or other Christian background. This does not mean Irish unity has automatically become a majority position. Religious background and voting behaviour are not the same thing, and middle-ground voters, secularisation, class and economic risk all matter. But it changes the political psychology. Northern Ireland was built on the expectation of a stable Protestant unionist majority. When that majority is no longer stable, the constitutional balance becomes more fragile.
Brexit made that fragility more visible. Leaving the European Union was a UK-wide decision, but Northern Ireland’s geography made it impossible to handle in an ordinary way. If the UK fully left the EU single market and customs arrangements, a hard border could have returned on the island of Ireland. If that hard border was to be avoided, Northern Ireland needed some form of regulatory difference from Great Britain. The Northern Ireland Protocol, and later the Windsor Framework, were the result of this trade-off. Northern Ireland remains inside the UK, but it retains special links to the EU single market for goods. This made many unionists feel that a border had been placed in the Irish Sea. It also showed nationalists something important: remaining in the UK does not necessarily mean being fully integrated into the same system as Great Britain.
After Brexit, Northern Ireland’s position became awkward, but also potentially advantageous. It has access to both the UK market and aspects of the EU market, yet it does not fully participate in EU decision-making. For business, this can be a benefit. For democracy, it can become new fuel for identity politics. Supporters of the Union can argue that Northern Ireland still depends on UK fiscal transfers, public services and welfare arrangements, while the tax, health, education and legal design of a United Ireland remain unclear. Supporters of unity can argue that Brexit pulled Northern Ireland away from the European direction preferred by many of its voters, while the Republic of Ireland remains inside the EU. Irish unity, in that framing, is not just a nationalist aspiration. It is a possible route back into a European political order.
Recent polling reflects this shift, but it must be read carefully. The Irish News reported on a poll commissioned by European Movement Ireland and carried out by Amárach Research in late March 2026. When the question was framed as support for a United Ireland inside the EU, 63% of Northern Ireland respondents said they would vote in favour, while 29% said they would vote against. The same poll found that, if the UK held a referendum tomorrow on rejoining the EU, 73% of Northern Ireland respondents would support rejoining. These numbers are striking, but they are not the same as an ordinary border poll. The phrase inside the EU changes the calculation for many voters.
Other, more conventional polling suggests that Irish unity does not yet command a stable majority in Northern Ireland. A late-2025 poll by the University of Liverpool’s Institute of Irish Studies found that, when the constitutional question was asked more directly, around 40.6% supported a United Ireland while 59.4% supported remaining in the UK. The 63% figure therefore should not be treated as proof that a border poll has already been won. The better reading is that when Irish unity is linked to re-entry into the EU order, Northern Ireland’s constitutional imagination changes significantly.
Northern Ireland may therefore leave the UK before Scotland not because everyone has suddenly become nationalist, but because several structural conditions coincide. Historically, its border is the unfinished part of the British and Irish settlement. Legally, it already has an exit mechanism recognised by the peace agreement. Demographically, it can no longer rely on a stable Protestant unionist majority. Politically, Brexit has widened the institutional distance between Northern Ireland and Great Britain, while making Irish unity easier to connect with EU membership. Scotland has a clearer independence movement and a stronger nationalist government tradition, but it lacks a separation mechanism already written into UK law. Northern Ireland is the reverse: the political consensus is not yet there, but the legal door is already open.
This is why a Northern Ireland border poll is relatively simple and direct in procedural terms. That does not mean it would be easy to win, or that a United Ireland would be easy to govern. It means the mechanism for asking the question is clearer. If the Secretary of State judges that a majority for unity is likely, a border poll can be triggered. If a majority in Northern Ireland supports unity, the Republic of Ireland would also need to make its own democratic decision. The hardest questions would come after the vote: taxation, healthcare, pensions, citizenship, policing, public spending and protection for unionist identity. The referendum is not the end of the problem. It is the gate through which the problem would move.
Whether Northern Ireland actually becomes the first part of the UK to leave still depends on economic design, public finances, guarantees for unionists, the attitude of the British government, preparation by the Irish government and the confidence of middle-ground voters. But among the 4 parts of the UK, Northern Ireland has the most institutionalised centrifugal force, the clearest legal exit and the strongest external anchor. The UK has often survived by keeping constitutional questions blurred. Northern Ireland has survived by putting consent into writing. If that consent begins to move, the same written settlement that preserved peace may become the route map for departure.
