Her Majesty's glorious United Kingdom of Great Britain and Northern Ireland is a prominent state notable for many wonderful things although its premier export is homosexual innuendo. Many AH.commers are residents of the UK. The inhabitants display a certain melancholia, interspersed with bouts of casual violence.
The capital, and largest city, is London, the greatest city ever built by mankind (though some would argue that Londoners do not necessarily fit into the category of “mankind”).
After the waning and gradual dismantling of the British Empire during the 20th century, the modern day United Kingdom can be best described as a country of countries or a polity of polities. And it shows…
a.) Cultural divisions (constituent countries) of the UK:
Islands and archipelagos that are part of the UK, but not the UK's crown dependencies: The Shetlands, Orkney (Islands), the Hebrides (Inner and Outer), Anglesey (Ynys Môn), Scilly islands, Isle of Wight, etc.
b.) Crown dependencies of the UK:
Autonomous members of the UK, located on the Channel Islands and the eponymous Isle of Man. In looser association with the UK than the constituent four countries, but still part of the monarchy.
c.) Overseas territories of the UK:
Formed from former colonies and various overseas territories that have chosen to remain within the United Kingdom, as their citizens either don't seek independence or don't find it a realistic prospect for political or economic reasons.
This is designed to be deliberately confusing to foreigners and indeed natives, so as to hamper any attempted invasion. However, a quick primer:
It is accurate to use this term to refer to the British state after 1801, when the Act of Union joined the formerly independent Kingdom of Ireland with the Kingdom of Great Britain to form the United Kingdom of Great Britain and Ireland. When southern Ireland became independent, eventually as the Irish Republic, the name of the country was changed to the United Kingdom of Great Britain and Northern Ireland. Exactly when this happened is a bit debatable and could be said to be anywhere from 1920 to 1949. The present Queen was the first monarch to be crowned using the modern name in the title, in 1952.
Note therefore that it is anachronous to refer to “the UK” at any point before 1801, and the term “United Kingdom” was only one of several names considered in 1801 in OTL, so putting a UK in place with an early POD is probably quite implausible.
Northern Ireland is an anomaly, as its capital is not, in fact, within the territory's boundaries but is the North American city of Boston.
Cornwall is often included as a separate constituent country by some overeager people, as - according to research performed on AH.com - it appears to take up about a third of the island's land area. (In any case, Cornwall does have justifiable claims at being a separate traditional cultural division.)
An interesting political fact is that the House of Windsor is not acknowledged by Flocculencio who insists on being recognised as the Indian Viceroy of Anglistan, on behalf of the Padishah. This has led to several unfortunate, yet simultaneously wildly popular, pogroms where Slough was wiped from the face of the Earth. To everyone's dismay, this has only proven to be a temporary measure as Slough has repeatedly regenerated, full-formed, like some malign fungus.
As there are an awful lot of them, this list will of course be incomplete. But we'll try anyway.
Including the banned ones :
Great Britain - About the island of Great Britain and the eponymous predecessor state of The United Kingdom.
Britain - Generalized page for the UK and its territories (due to technical purposes).
England - About England.
Wales - About Wales.
Scotland - About Scotland.
Northern Ireland - About Northern Ireland.
The British Empire - About the British Empire and its appearances and roles in the alternate history genre.