Originally Posted by
justapax
I think it's only Ireland that is EU but not Schengen (because of the CTA with the UK). I'm not an expert, I stand to be corrected.
I think you are correct. The pre-Brexit situation was that both the UK and Ireland were outside of the Schengen area, so perhaps even without Brexit, UK passport holders would still have needed to go through some sort of entry/exit check.