Six people are being questioned in Dublin after the seizure of drugs with a street value of up to IR£12.5m.
The drugs were found in the door panels of cars that left ferries from Holyhead at the Dublin port of Dun Laoghaire.
The haul includes heroin and cannabis and is now being analysed by experts.
Three men and three women, aged between 19 and 58, are being questioned.
One of the women has an address in the Isle of Man. The others are understood to be from Manchester.