After Brexit UK established manufacturers and distributors of goods who sell to the EU, will be subject to customs processes and may be also subject to customs duties. In the most likely scenario of a trade agreement between the EU and the UK, there would be customs duties on most machinery. The average rates are between 0% and 7% under the default EU third country tariff regime.
Assuming as seems reasonable, that a free-trade agreement will be negotiated with zero rate duties on almost all machinery, then customs processes and procedures will, nonetheless, continue to apply. For goods imported from outside the EU and UK such as from countries with no trade agreement such as China or India, there is the possibility of a double charge to customs duty, even in circumstances of a zero tariff-free trade agreement. This is because goods of UK origin only would qualify for the likely zero rates of duty.
Goods imported, for example, from China may be subject to UK duty for example, at 6.25% (a common rate for many machinery items) and again subject to customs duties duty at 6.25% on importation into the EU. There is limited scope only for customs reliefs for goods temporarily present in the UK having been imported from outside Europe, where they are later sold into the EU.
An Irish established distributor into the EU who imports from countries with which the EU has a free-trade agreement, such as for example, South Korea and Japan, may import into the EU at the reduced or zero tariffs provided in the relevant agreement. The UK may or may not be able to replicate the EU trade agreements with such countries on the same terms.
An Irish established distributor into the EU who imports from a country with which there is no free trade agreement such as for example China, India or the United States, is subject to one set of customs duties only. Having cleared the goods into Ireland, it may distribute them throughout the EU without further customs duties, controls and processes. The goods are in free circulation and may move to other EU states freely without import or export declarations or requirements for a certificate of origin.