The Entente Cordiale, between Britain and France, signed over a century ago, was mean't to prevent war in Europe and anglo-french rivalry in Africa.
It failed. It didn't prevent WW1 or the enthusiastic French collaboration with Nazis in WW2.
But it continued in fictionised form, post war, saving French blushes for colaraboration
Post-Brexit, the true Vichy character of France re-emerged in French letter to the EU, demanding that the EU "punish" the UK for the "crime" of voting to leave the EU. '
The issue is 40 fishing licences rejected by the Crown Dependency of Jersey. The French believe that this fraud should be over-looked. The British believe that caving to fraud invites more fraudsters to try it on.
Why is France willing to risk their relationship with the UK over 40 fraudulent boats? Brexit.
This isn't about fishing, it's about Brexit. The fact that the British were able to vote to leave, when the French arn't allowed this sort of democracy.
France blockaded the UK in X-mas 2020, supposedly because of a covid variant (which was already in France, rendering it moot).
The British held their fire, but once it became clear that the French were being spiteful, everything changed.
New threats for a blockade have met with a stern response.
If the EU can stop you defending the homeland, what else is left?