VISITORS to Ireland can raise eyebrows by referring to Britain as “the mainland”. Yet the ferries that connect the two islands are the Republic’s main surface life-line. Not only does Britain account for 12% of Ireland’s external trade in goods, but the “land bridge” via the Channel Tunnel is the quickest route for lorries between Ireland and the rest of the European Union. The continental EU, representing 38% of trade in goods, is Ireland’s biggest market.

Lorries can drive onto a ferry from Dublin or Rosslare to Britain at 9am and be in Paris by midnight, says Verona Murphy, president of the Irish Road Haulage Association. Direct ferries to the continent, from Rosslare to Roscoff or Cherbourg in France, take at least 17 hours for the crossing alone. They also cost more: about €1,000, compared with €540 for the Irish Sea and Channel Tunnel crossing.

But if Britain leaves the EU next year without an agreement on trade, customs, immigration and food safety, it would mean reintroducing physical controls on trade from Ireland. That would make the British route much slower and more expensive, and could rule it out for Irish “just-in-time” trade.

Ms Murphy’s own firm is a perfect example. It operates four refrigerated trucks that bring Irish meat to Italy and return with fresh herbs. “From the time the herbs come out of the ground to the supermarket shelf in Ireland it takes about five days, and you are then left with a shelf-life of three to five days,” she says. Making the trip longer reduces the shelf life. Beyond a certain point, it could render the whole enterprise unprofitable.