Sirboeing
i asked a European agency about the requirements regarding UK to EASA at PPL level and it was as follows: 5 hours dual, skills test, EASA medical and ground study followed by a test. I’m just considering whether it’s worth the hassle for a few hours every year. If you’re in the UK I believe there’s a club at Stapleford that have EASA approval and likewise there is an AME at LGW who has AME approval. Appreciate you’re asking about ATPL but maybe try them.
As for the politics there is no escaping the fact that the CAA wanted to remain in EASA so I can only assume that the reason they could not was down to political considerations regarding the ECJ having jurisdiction. There was a RAes paper with detailed analysis so it’s not like these problems weren’t foreseen. Brexit, IMHO, is a mess and was always going to be so as divorces often are. The Brexit voting public should have conducted a thorough cost/benefit analysis before voting yes. The benefits, if you can call them that, might have been obvious but the true cost is only emerging now.