Non-tariff barriers will also cause disruption. The rules of origin are extremely complicated and I have copied and pasted an example below
Rules of origin are criteria to define where a product was made, and thereby ensure that the correct tariffs and other regulations are applied. The WTO Rules of Origin Agreement requires that these rules are administered in a consistent and impartial manner although, as with tariffs, countries can adopt different rules where trade preference agreements, such as a customs union, are in place.49 WTO members must notify the Secretariat of what their rules are; as a member of the EU, the UK currently applies the EU rules of origin.50 Importers present proof of origin to the customs authority, in line with that country’s rules. This issue is explored in more detail in the EU Committee’s report Brexit: trade in goods.51 There are no origin requirements for trade within the EU, but when the UK leaves the customs union, producers will need to meet whatever origin regime is put in place. This will apply even if a trade agreement is reached, as producers will need to demonstrate their product is eligible for preferential trade terms. Rules of origin can be problematic for products that have inputs from different countries; depending on the approach taken to origin requirements products could be excluded from the benefits of any free trade agreement negotiated. The Food and Drink Federation gave the example of a frozen pizza made in the Republic of Ireland, but with flour milled in the UK from grains bought from Canadian, US and UK growers. Failing to meet origin requirements would mean the flour would be subject to EU MFN tariffs when imported from the UK; the pizza would then also be subject to tariffs if exported for sale to the UK.52