but if you are able to drive to a country most often you don't even get checked at the borders!In every EU country except for Ireland there is immigration control when you exit. Same in the UK, your pass through border control/immigration only when you enter, no exit checks. Same thing when departing from Canada/USA. So for example when flying from Ireland you can use any passport you like as long as you comply with your destination's country visa requirements. That's what airlines check for.