Seems like this is the battleground.
The EU wants access to fish in UK waters. The UK has no interest in letting European vessels in.
This has nothing to do with trade. It's about access to food resources. I guess the French, Germans and Spanish don't want to pay UK trawlers for fish.
For myself, I like the idea that we have an economically feasible maritime economy. I hope we end up funding a stronger navy with part of it.