In that case your old CAA-issued EASA licence has become a UK licence as you suspected. it is no longer valid for EASA registered aircraft. There is a transition period to Dec 2022 where the CAA will continue to accept EASA certificates and ratings, with some caveats so, if you did an EASA rating with an EASA ATO that had its approvals in place on exit day (not one of the UK ATOs that gained EASA accreditation the day after) then the CAA should accept it and put it on your UK licence. Similarly the CAA will obv accept a rating from a UK ATO.