Hello Bushdodge,
I am a UK FI/A PPL through CPL and ME IR etc. My class 1 has
OML and I have an SSL added since early 2020 which allows me to instruct up to CPL in SPA aircraft under
5700kgs. The CAA issued an email to me regarding Class 1 OML and Instructing/Examining CPL which went to all AME's I understand. My last medical in Aug I still have the SSL.
The Instructor should talk to his AME who should have had that email too, He/She could send message down the the CAA to request addition
of SSL for the reason you mention.
Thats what mine had to do and If its like me AMS emailed me a letter to tell me it was approved and sent a new certificate via post with the SSL added. My ATPL
is now UK CAA not EASA as I did not SOLI.
Whether the CAA have changed the policy of adding the SSL I am not sure but as I still have this on my latest Certificate I would think its possible.
Regard's,