The UK CAA did make it clear on the Brexit site for almost 2 years that the U.K was leaving EASA with possible future mutual recognition which has not happened yet. People did have time to transfer licenses out if they desired, and the U.K CAA did say you could get a U.K license back post Brexit.
If an employers contract required a U.K license, perhaps employees or BALPA reps could have discussed transferring prior to Ireland or somewhere else in the years prior.
A few people now are stuck with the U.K license and hopefully the U.K CAA or department of transport are trying to sort out the mutual recognition.
If UK pilots no longer have the right to work in the EU, no mutual recognition as of yet, and the CAA wants revenue. Perhaps the CAA need to require aircraft / bases in the U.K to be on the G reg, with UK license holders and U.K residency.