Just a notion:
Instead of a United Kingdom how about a United British Republic of England, Wales, Ireland, Scotland, Isle Of Man and the Channel Islands.
Each Nation has control of 90% of it's own affairs except foreign and trade affairs which are conducted through the federal parliament in London.
Each nation also has is own assembly for their own affairs:
England: York
Scotland: Edinburgh
Wales: Cardiff
Ireland: Dublin
IOM: Douglas
Jersey and Guernsey have their own states.
The federal government has a president as head of state who selects a first minister and cabinet.
Each "regional" assembly have their own elections.