Does the post not say his EASA licence was issued in 2013? My interpretation, he can use this EASA licence until 31/12/2022.
Based on that, the poster has the option of doing an FI course with an EASA ATO in the UK or outside, getting his licence endorsed, then moving across to a UK licence at some point in the future. All valid ratings/certificates move across.
- or -
Get the UK licence now, use a UK ATO for the FI course, and end up with the FI on the UK licence only.
Regarding what is endorsed, I've based my post on what the CAA website linked above says:
What will be issued on the UK Part-FCL/BFCL/SFCL Licence
All privileges endorsed on your licence at the time of transfer from the UK will be endorsed onto the UK Part-FCL/BFCL/SFCL licence. Any additional privileges from the EU Part-FCL/BFCL/SFCL will also be endorsed onto the UK Part-FCL/BFCL/SFCL, excluding any National or Restricted Ratings. Any valid ratings will be annotated on the certificate of revalidation, with any expired ratings being removed to the back of the licence.
I always try to back up what I say with the source hence the CAA website links, do you have a difference source that contradicts mine? I'd like to be accurate in the advice I give...