Both Scotland and England gave up their sovereign status when the Acts of Union were enacted, to form the United Kingdom of Great Britain.
Basically, Scotland, Wales, England, and Northern Ireland, are nations which comprise the United Kingdom of Great Britain and Northern Ireland, which is the sovereign state.
> Are not Scotland, Wales and England each countries though?
Sure, but in a sense where UK “countries” are a thing somewhat like US “states” (but somewhat less, in that neither is independent, but US states are notionally sovereign nevertheless.)
The UK is the entity which is a sovereign and independent entity.
Both Scotland and England gave up their sovereign status when the Acts of Union were enacted, to form the United Kingdom of Great Britain.
Basically, Scotland, Wales, England, and Northern Ireland, are nations which comprise the United Kingdom of Great Britain and Northern Ireland, which is the sovereign state.