the CAA cannot add it onto my national license - happy to be corrected though, as it is still a mystery after well over a year waiting to hear back from the CAA.
152.—(1) Subject to article 172, the CAA or a person approved by the CAA for that purpose
must grant licences of any of the classes specified in Part 1 of Schedule 8, authorising the holder
to act as a member of the flight crew of a non-EASA aircraft registered in the United Kingdom, if
it is satisfied that the applicant is—
(a) a fit person to hold the licence; and
(b) qualified by having the knowledge, experience, competence, skill and physical and
mental fitness to act in the capacity to which the licence relates.