Very well. Your answer is "No." You didn't say that before. It looks like we will never know what festive wants. Bodge doesn't know what he wants so he can't tell us.
In that case you must have border controls and check that people entering the UK from the EU are suitably qualified to allow them to enter. You cannot have open borders if you wish to control entry.
The Republic of Ireland is a part of the EU.
Therefore you want border controls between RoI and the UK.
NI is part of the UK.
Therefore you want border controls between RoI and NI.
That was easy.
John, you're either not listening or you're as thick as a whale sandwich.
The common travel area stands regardless of wether we or Ireland are in the eu.