Blame the uk consumer and govt for a: not buying UK produce and b: for having so many unnecessary regulations.
We used grow flowers and toms, neighbours similar, all but one have gone to dust, south facing valley, perfect for growing but no one does, across the valley was a fruit farm.... several holiday lets now,
We have huge input costs, not least energy, we tried wood chip, bio fuels any but in the end, it was all too expensive.
Thats all on the UK, nothing to do with with the EU.
I can buy Whiting in France, caught in UK waters, can't get it here but i can buy Basa imported from SE Asia.... its on us and greed by the unregulated supermarkets.
France is over 100% self sufficient in food, the UK is around 65%.