Well... the UK isn't a country.
Its very simple - the United Kingdom is the Sovereign State, within the United Kingdom are various Nations & Islands. Including the island of Great Britain (Which includes England, Scotland & Wales), Northern Ireland, Gibralta, Fauklands etc. None of the states within the United Kingdom hold any sovereign power.
England has no sovereignty of its own, neither do Wales, Scotland or Northern Ireland. Like each state within the USA. Wales, Scotland and Northern Ireland have devolved parliaments where they can make local laws on education, infrastructure and healthcare - so long as they don't go against laws that govern the UK. England is only represented in the UK Parliament, which is why some fuckwits want there to be an English Parliament too.
The UK is the Sovereign Power, the others are just parts of that Sovereign Power. Simple.
To be clear this is the definition of a Sovereign State
A sovereign state, or simply, state, is a state with a defined territory on which it exercises internal and external sovereignty, a permanent population, a government, and the capacity to enter into relations with other sovereign states.[1] It is also normally understood to be a state which is neither dependent on nor subject to any other power or state.[2] While in abstract terms a sovereign state can exist without being recognised by other sovereign states, unrecognised states will often find it hard to exercise full treaty-making powers and engage in diplomatic relations with other sovereign states.
As set out by the the treaty of Westphalia in 1648.
I do have a bit of a chip on my shoulder about this because so few people understand such a simple thing.