Basic geographical knowledge shouldn’t be considered a form of pedantry, especially when it’s your home country in question. The "British Isles" is a geographical term for the archipelago (including Ireland), while the "UK" is a political entity (England, Scotland, Wales, Northern Ireland). The British Isles covers all islands, whereas the UK is just a subset of them; Ireland is geographically in the Isles but is a separate, independent nation.
I'm referring more these days to Britain rather than the UK - though Uk is more accurate since the full name is The United Kingdom of Great Britain and Northern Ireland, but it's a bit if a mouthful. I get narked by those who assume Great Britain represents some sort of imperial age chest beating when in fact "great" just refers to the geographically largest island in an archipeligo. Similarly Francophiles who object to the "English" channel. If they'd paid attention at school they'd know that it is the convention to name a strait between an island lying off a larger land mass after the the island whose existance forms the strait. It doesn't imply any kind of territorial claim.
