You mean like the time you chopped Ireland in half?
That isn't what happened at all.
The Union of Great Britain and Ireland happened a long time ago and everyone was happy with it. Well almost everyone. Everyone who matters. Henry VIII was the first king of Ireland and he did a good job. Probably.
Anyway, in 1918 the Irish vote in their droves for Sinn Fein.
Being the polite and generally lovely people that we are in the UK, by 1921 we had let the rest of Ireland be an independent country. That's what they wanted. They got it.
But look how Northern Ireland voted. For unionist parties. So we said, Ok, you want to stay, you can stay. We gave absolutely everybody what they wanted. But the greedy nasty Irish wanted more. They wanted to rule over the northern Irish too, despite their not wanting to be Irish. And the Irish resorted to terrorism and the USA decided to fund that terrorism because Americans are fundamentally wicked.
So we never chopped Ireland in half. We left the half that wanted to leave leave, and let the half that wanted to stay stay. ¯\_(ツ)_/¯ Do you have a better suggestion as to what the British should have done?