The fish debacle ( the UK refusing to license EU-based ships).
There are lots of licensed EU fishing vessels. Note that Jersey isn't actually a part of the UK, technically it's a Crown Dependency. Anyway. The full story of the dispute is much more complicated than that:
https://en.wikipedia.org/wiki/2021_Jersey_dispute
Summary:
- After Brexit an amnesty period was agreed before the new fishing permissions were enforced on UK/Jersey territorial waters.
- French fishermen reacted by adopting unsustainable fishing techniques like aggressive trawling. Basically trying to extract as much marine wealth as possible before they were restricted. "Young accused French trawlers of "breaking the spirit of the amnesty" and that due to recent dredging by French trawlers that Jersey's marine ecology "won’t take this for much longer and, if it goes on, we will have to close the area off for years". This hadn't been anticipated in the agreement and appears to have poisoned relations from the get-go.
- The agreement involved granting licenses to fishermen who had been fishing there previously and could evidence that. The French authorities weren't submitting valid evidence to the Jersey authorities (blaming bureaucratic screwups like lost documents).
- Because the evidence wasn't meeting the requirements, licenses weren't always being issued quickly.
So far, ordinary bureaucracy. It should have never really reached public attention at all, as it could have been sorted out between the local authorities. Unfortunately what followed was this:
1. Blockades of Jersey harbor by the French fishermen, with the French government doing nothing.
2. French boats were repeatedly caught illegally fishing, claiming they'd been told by the French government they could fish wherever they wanted. See the trawling problems above.
3. Shortly after, the French government banned Jersey fishermen from landing fish in France. No justification was given. This was in violation of the agreement and Jersey thus said it'd appeal to the EU Commission. That was not only ignored but the French simply escalated the ban to include all freight movements, again, in plain violation of the agreements.
4. The French government then escalated again and threatened multiple times to cut off Jersey's electricity supply in retaliation.
From the UK's perspective this was all well out of proportion to the scale of the problem. Also it involved unilateral violations of the agreement by France, no workable suggestions for how to do things better and after that an MEP argued that it should be escalated to full blown trade sanctions. Without passing judgement on which side was "right" in this dispute it's obvious why the UK would want to diversity energy supplies away from the EU.