I'm not certain it's still the same, but back in 2014 when I bought mine SEAT shipped UK orders from Barcelona to either Sheerness - where mine went, or Port of Tyne for northern counties. I don't know if Irish orders would be shipped separately or not but I imagine they may be. My car came over on a ship called Galicia... Very, very slowly.
SEAT martorell is linked to Barcelona docks with a dedicated train line.