That depends entirely about which CAA you are talking: If you meant the UK CAA, then yes, it'll be an initial. If it is some other, then I would contact an AME of a few countries.
If you did it in Germany for example, you could do a German CAA (LBA) renewal, then get a CAA UK renewal a minute later from the same examiner.
Else, get the form from the CAA UK, take it out to the AME, once he has filled it in, you pay £20 in Gatwick, and there is your CAA UK medical.
This procedure does not depend on the licence held.
regards, I.