A common misconception: the UK's four constituent parts—England, Wales, Scotland, and Northern Ireland—are often called "states." They're not. Here's the distinction.
The United Kingdom of Great Britain and Northern Ireland (UK) is a single sovereign country in international law. It holds one UN seat, one passport, one military, one foreign policy.
England, Wales, Scotland, and Northern Ireland are countries (or nations) that together form the UK. Each has distinct identity, history, legal systems (Scotland's is separate), and varying degrees of devolved governance:
In political science, a "state" = sovereign state. Subnational entities (like U.S. states, German Länder, Indian states) are federated states within a federal system. The UK is a unitary state with devolution, not a federation. Its parts are countries, not states.
Great Britain = the island containing England, Wales, Scotland. UK = Great Britain + Northern Ireland. Don't conflate the terms.
So: four countries, one sovereign state. Call them countries—or nations—and you'll be accurate.