The problem actually is that The United Kingdom of Great Britain only came into being as a result of the 1707 Act of Union, when the Kingdom of Scotland and the Kingdom of England joined together as a single political unit under one parliament.
If the Act is repealed then there will once again be a Kingdom of Scotland and a Kingdom of England. There will no longer be a United Kingdom.
Wales is not a Kingdom, neither is Northern Ireland.
So no kingdoms will be united anymore, will they?
Might be easier to go down the Yugoslavian route.
How about the Former United Kingdom?