I think both sides overlook a fundamental issue with trade. All this talk of barriers going up, no trade, trade deals taking years . (all Threats and Fear statements by the way) overlooks a fundamental issue. Vested interests run trade and commerce. No way will they want things to stop working. The ships would stop running, mines would stop mining, smelters would stop smelting, docks would have nothing to load/unload, logistics would have nothing to deliver. etc etc. Europe and possibly the world would go into recession. Vested interests wouldn't have that. How do countries with no trade deal manage to trade?
No I can confidently predict cars will still be made and still astonishlingly be sold. Salad crops will still be grown and sold as will beef and French wine. Too much at stake to not do so.
It's about "free trade deals" - not no trade deals.
If there is no "free trade deal", then when you export to a country you have to pay import tarrifs and duties to that country. These can be anything from 0% to 1000%. The effect is that it pushes up the price of your exported goods to the customers in the destination market. This has the effect that locally produced goods appear 'cheaper' to the customer, so they tend to stop buying your goods, and start buying from elsewhere.
It's easy to do with some goods - milk, cheese, basically anything farmed. However, if the end customer is intent on buying premium brands, like Scottish Whisky, or Pomerol wine, or BMW's or Somerset Cheddar Cheese and Scrumpy then they will just pay the new artificially increased price. Exports won't stop, they just become more expensive, which negatively affects quantities and company profits.