fishes According to R North, a leaver who has studied the possible consequences of Brexit over some years,
all previous arrangements re imports - and exports - are null & void unless there is a specific deal to change this.
The UK will no longer be able to treat imports from EU countries differently to those from other WTO member countries, regardless of whether e.g. companies have existing contracts, or whether trade was formerly "frictionless"
Hence, the UK would either have to wave through goods from all countries or perform comparable checks on all countries,
according to the WTO scale of how many checks for which region, e.g. imports from some groups of countries might need to have 20% of consignments inspected; others might need 50% inspected.
In the case of food, he says the UK would presumably choose to wave through all food from anywhere, without checks, as an alternative to logjammed ports.
RNorth thinks the govt will have to use emergency powers to only allow empty lorries to travel to Calais etc, to reduce delay at their end.