I get that Britain kind of ignores their part in Irish history a lot but how can you not even now the basic geography of your own country?
Welcome to the English state education system. Geography is an afterthought. Politics barely exists. History covers the Tudors and the World Wars over and over and not much else. All but abolish Critical Thinking and lambaste Media Studies (no one needs to know what the papers do to this country!). Keep the state school kids ignorant and lacking in curiosity... Not that that's an excuse not to educate yourself in your free time, of course, but if there's no curiosity, there's not much drive.
Going off on a tangent a bit, but I once spoke to another English woman who didn't know why Australia speaks English. No idea that it was colonised by Britain, or who was there before us, or why it's now predominantly white, she'd just "never thought about it before".
Back on tangent, I find even when people here in England talk about the UK, they often forget about Northern Ireland. Not deliberately "forget", but genuinely forget it exists. It's only since the Brexit referendum that it's become apparent that our government did, too.
I've also come across more than one person who calls Ireland "southern Ireland". 