>>2600011It’s not an obscure law; it’s the legal framework of the state.
The UK uses the word “country” as one might use the word “nation”- that is, to refer to a group of people and their homeland. Thus, Scotland, Wales, and England are constituent countries of the United Kingdom, with varying degrees of autonomy.
For instance, Scotland has always been more independent (they’re like Texas or Quebec), so they have their own parliament, their own royal flag, their own chivalric orders, etc. Meanwhile, England has no devolved parliament and is directly led by the UK national parliament. Wales is sort of an intermediate level of autonomy between England and Scotland, and Northern Ireland is a province, but not a country (Although, before 1922, Ireland was considered a constituent country of the UK).