Our food trade with the EU is tariff free. This helps EU exporters compete in our market. They sell us 3.4 times as much as we sell them in the wider food and drink category. Whisky is our biggest export. Our sales of meat, dairy, fruit, vegetables and cereals are low. Years in the CAP with small milk quotas, beef bans and grants to remove orchards led to substantial reductions in UK farms home market share. We cannot now produce nearly enough temperate food to meet our own needs.
Some now argue we need to adopt again all the rules and controls the EU places on farms and food producers so we could export more to the EU without some of the border frictions the EU imposes . So what could we produce more and what would they buy? Our sales did not fall post Brexit.
The main reason the EU wants more controls over UK farming is their wish to keep out cheaper non EU food from competing with their exports to the UK.They also want to block innovation in the UK that could lead the UK to cheaper and better food at home. They veto genetic modification.