Ireland & United Kingdom
Ireland and the United Kingdom share the closest relationship of any two states in Europe — a common land border, a free-travel zone that predates both countries' EU membership, and a peace process that both governments co-guarantee. Brexit strained that relationship more than any event since partition, but the Common Travel Area and the Good Friday Agreement have held.
How the relationship developed
Acts of Union merge the Kingdom of Ireland into the United Kingdom of Great Britain and Ireland.
Anglo-Irish Treaty ends the War of Independence; the Irish Free State is established, partitioning the island.
The Common Travel Area is established, allowing free movement between Ireland and the UK that survives to this day.
Ireland and the UK join the European Economic Community together.
The Good Friday (Belfast) Agreement, co-guaranteed by Dublin and London, ends three decades of the Troubles in Northern Ireland.
The UK votes to leave the EU, reintroducing a question of borders and trade the Good Friday Agreement had set aside.
The Northern Ireland Protocol and its successor, the Windsor Framework, manage Northern Ireland's unique post-Brexit position — inside both the UK customs territory and the EU single market for goods.
Key issues in the relationship today
The Windsor Framework
Northern Ireland effectively remains in the EU single market for goods while staying part of the UK customs territory — a compromise that avoids a hard border on the island of Ireland but creates new checks on goods moving from Great Britain to Northern Ireland.
The Common Travel Area
Irish and UK citizens can live, work, study, vote in some elections, and access public services in each other's country without needing a visa or residence permit — arrangements that survived Brexit intact.
Northern Ireland's constitutional future
Under the Good Friday Agreement, a "border poll" on Irish unity must be called by the UK government if it appears a majority in Northern Ireland would support it — see our United Ireland tracker for current polling.
Trade after Brexit
The UK remains one of Ireland's largest trading partners despite no longer sharing EU membership, though new customs and regulatory paperwork has added friction, particularly for smaller exporters.
The diaspora connection
Millions of people in Britain have Irish parents or grandparents, the legacy of successive waves of Irish emigration since the 19th century. Irish citizens in the UK can vote in UK general elections, and UK citizens in Ireland have equivalent rights — a reciprocity that predates both countries' EU membership and continued after Brexit.
A UK opinion polling tracker — Westminster voting intention, party leader approval, and by-election results — is in development for this page.