Border controls in Irish airports are in effect for both jurisdictions and facilitate the absence of such controls in London and other UK airports. In effect the British and Irish authorities operate a " mini-Shengen." The CTA is for UK and Irish citizens only so there would be nothing to stop the Irish authorities having a separate line for CTA eligible arrivals. I make a point of showing a driving licence to prove I am an eligible person for CTA purposes. There are anomalies in the system mostly caused by the land border with Northern Ireland that are too politically sensitive to touch. We should stay away from Shengen. The CTA has worked well over the decades and I see no need to change.