"It will of course be necessary for the fruit, vegetables, cheese, meat, etc imported to Ireland from Europe to come via France or the Netherlands rather than through the UK after Brexit, because otherwise these imports would be hit by two lots of tariffs - one to bring them into the UK from Europe, the second to reimport them into Ireland (ie Europe again) from the UK."

WHY?

The Convention on International Transport of Goods Under Cover of TIR Carnets (TIR Convention) is a multilateral treaty that was concluded at Geneva on 14 November 1975 to simplify and harmonise the administrative formalities of international road transport. (TIR stands for "Transports Internationaux Routiers" or "International Road Transports".) The 1975 convention replaced the TIR Convention of 1959, which itself replaced the 1949 TIR Agreement between a number of European countries. The conventions were adopted under the auspices of the United Nations Economic Commission for Europe (UNECE). As of January 2018, there are 73 parties to the Convention, including 72 states and the European Union.

The TIR Convention establishes an international customs transit system with maximum facility to move goods: