'United Kingdom of Great Britain and Northern Ireland' is just the formal name of the country. Most people would say Britain or UK (or even England) for short. (Just as people are unlikely to say 'Federal Republic of Germany' and 'Hellenic Republic' Instead of Germany and Greece)
Although it's not really a country in the strictest sense. England, Scotland and Wales are countries on the largest island of the British Archipelago, which is called Great Britain (great = largest).
But England, Scotland and Wales and Northern Ireland have been united under one monarch so they are a united kingdom.
So altogether it is the United Kingdom of Great Britain (the whole island) and Northern Ireland
Which means: The whole of the island of Great Britain and some of the island of Ireland united under a king or queen.
So I would put 'UK' or 'United Kingdom'.
Northern Ireland is not the smallest country in Britain. Northern Ireland is not in Britain. Britain is an island consisting of England, Wales and Scotland. Northern Ireland is on the island of Ireland. Wales is the smallest country in Britain. Britain and Northern Ireland together form the United Kingdom. Northern Ireland is smaller than Wales, so it is the smallest country in the United Kingdom.
United Kingdom of Great Britain and Northern Ireland.
Great Britain is comprised of England, Scotland and Wales. When Northern Ireland is included, the country then gets its full title of 'The United Kingdom of Great Britain and Northern Ireland'.
It is part of the United Kingdom of Great Britain and Northern Ireland.
Northern Ireland is a part of the United Kingdom of Great Britain. In contrast, the southern portion of Ireland (the Republic of Ireland) is its own country.
Northern Ireland, which is on the island of Ireland.
England is a country that makes up part of the United Kingdom, along with Scotland, Wales and Northern Ireland. Great Britain is the island that England Scotland and Wales are part of. The United Kingdom is Great Britain and Northern Ireland. Northern Ireland is on the island of Ireland, so Great Britain does not include Northern Ireland.
Great Britain is part of the sovereign state of the United Kingdom (of Great Britain and Northern Ireland)
Great Britain, which is comprised of England, Scotland and Wales. However, if you add Northern Ireland, the country then has its full name of The United Kingdom of Great Britain and Northern Ireland which is what it is called on a British passport.
Northern Ireland
The United Kingdom of Great Britain and Northern Ireland.
It is set in the United Kingdom of Great Britain and Northern Ireland