I've been pondering this. How can we get the United Kingdom to break apart peacefully where Scotland, and England are entirely independent of one another. Bonus points if Wales and Northern Ireland gain independence as well. Northern Ireland can be united with Ireland if you so wish.
England must remain a constitutional monarchy with the current Royal Dynasty at the helm, while Scotland can be either a constitutional monarchy or a republic, but must be a liberal democracy. The POD can be no earlier than World War I and no later than the Falklands War.