In the more than forty years that Britain has been a member of the Common Market and European Union much has changed that cannot be easily reversed. One of the foregoing would be the way that products are handled, transported and stored. Those changes many believe are these days fundamental to our way of living and are "wrapped up" in what is widely known as "Just in Time "distribution systems"
From the comments made on this forum, I believe there are some who post that do not understand the nature of those "Just in Time delivery systems" (JIT) and how vital they are in our modern economy.
If we take the example of a young parent buying products for the family at a supermarket, that supermarket holds very little stock (if any) of those items. In that, what customers see on the shelves are often the entire stock that the retail outlet is holding. However, as the items are passed through the checkout the sold items are placed on the IT system for replacement on the next scheduled daily delivery.
The above, in what is known as a "call over" is sent by the system to the supermarket's suppliers who at a set time of day/night will load vehicles and send them to the supermarket's distribution centres. At those centres, the vehicles arrive at a set scheduled time,
The Distribution Centre in what is known as a "cross-dock operation", handle the cages or pallets immediately and the supplies are unloaded, sorted to the retail outlets they are assigned to, mixed with other products arriving in the same mannerand reloaded onto vehicles (at times the same vehicles that brought the products in) to be sent to the retail outlets again arriving at a scheduled time for shelf restocking by those stores.
The delivery time is set to be just in front of the time the retail outlet would be running out of stock on the shelves, hence the name " just in time" (JIT).
The above takes place with almost all fast turnover products into retail and many large factory production lines in Britain and across the European Union.
However, anyone can imagine the "chaos" that will ensue should those vehicles carrying products on JIT delivery schedules begin to be delayed for an unknown number of hours at ports while customs checks are made.
I would suggest that the whole JIT transport system would quickly collapse with huge increase costs to consumers in Britain and the loss of many thousands of jobs as producers and suppliers move to EU countries. In that, following Brexit the EU is obviously to be the far larger market as compared to Britain, and where JIT systems will still exist within and between those EU countries.