You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
OK, so after centuries of movement the British Isles are united and the boundaries shown below are the ones which stick. The King of Ireland is always referred to as High King while both Wales and Scotland are just ordinary Kingdoms.
The Isle of Mann is a territory outside of the Four Kingdoms but is always a territory controlled by one of them until the unification. Eventually in the modern world Britain is forced to devolve power to them with the current boundaries. England is split however into equivalent earldoms making the title of Kingdom kind of a glory thing but Ireland's provinces have similar positions and the existence of High Kingdom is of no administrative meaning.
But my question to you is how do these boundaries come about? England consider themselves to be English and speak English as a first language. Welsh and Scots Gaelic are heavily spoken in the respective Kingdoms while Eastern Ireland has bilingual speakers mostly.
The idea the the far North of England should be Scottish and the North Bank of the Seven Estuary Welsh would be laughable.