Not convinced.
It looks like it's more about the relative strength of
national employment law (the
Code du Travail in France):
https://www.thelocal.fr/20220318/why-did-po-ferries-axe-uk-jobs-but-keep-its-french-workers/
https://news.stv.tv/scotland/staff-replacing-sacked-po-ferries-workers-face-poverty-pay-union-claims
UK employment law (which has not changed since we left the EU) mandates notice periods, consultation and so on, but it all sounds much weaker than the hoops employers in France have to jump through. The legacy of Thatcher and New Labour.
In any case, P&O rode roughshod over UK employment law in this case.
I've learned a lot reading this thread, especially from
@Richard Lines. I had no idea that seafarers' terms and conditions could be so appalling. The comments about some hourly rates being a fraction of the minumum wage are especially shocking.
Maybe that's where we should direct our anger. Like the TU rep said,
solidarity.