You say they check passports between Dublin and GB, but I'm a Northern Irish guy who took the car over the ferry from Belfast to Stranraer then back from Holyhe

You say they check passports between Dublin and GB, but I'm a Northern Irish guy who took the car over the ferry from Belfast to Stranraer then back from Holyhead to Dublin, I didn't even think about bringing my passport with me. The height of customs was on the Dublin from Holyhead side, they got me to roll down my window and asked me what my nationality was.