True,but they were colonies that were under the British Empire, rather than being made part of the UK, that slowly gained dominion status granted self-governance that eventually came full governance. The United Kingdom was formed around 1707, between England and Scotland. Ireland was joined in 1801. Ireland left the United Kingdom in 1921 coming a dominion until becoming a republic and cutting all ties to the monarchy.

My scenario doesn't abolish the United Kingdom, it abolishes it as a country, not as an entity. Which would be either largely symbolic, or something closer to the EU in design