Christopher

But EU passports are still primarily national passports – so if you're entitled to both a British and an Irish passport you can still have both, obviously. EU countries' passports are issued in a common format (more or less), but they are issued by the national authorities to those people whom the country concerned considers to be citizens.

The situation vis à vis Irish citizenship for those born in Northern Ireland is slightly complicated, as noted above, but today (putting it simply) such a person is entitled to claim Irish citizenship on the same basis as a person born in the Republic of Ireland. Of course, there is no requirement for them to do so, and they won't be regarded by Ireland as citizens unless they do something that only an Irish citizen can do. And people born in Northern Ireland have the same claims to British citizenship as people born in the rest of the United Kingdom.