Strictly speaking the UK-ROI CTA only applies to UK and ROI citizens. And you still need to show your passport / valid ID to show that immigration control (questions such as purpose and length of visit) does not apply to you.
So on arrival into Ireland you will see an immigration officer.
If you have a visa then you should make efforts to seek out an immigration Officer on arrival back into the UK so your departures and arrivals can be correctly recorded.
Last edited by UKtravelbear; Jun 2, 2022 at 8:19 pm