You have a UK NPPL - that's not the same as a UK PPL. SSEA ratings only appear on an NPPL. You can't put an SEP rating on your licence. You need to look at CAP804 to see if you meet the requirements to gain an EASA LAPL from your NPPL and then look at Part-FCL to see what you need to do to get from a LAPL to a full PPL and SEP rating. I don't think that there's a direct path from NPPL to full PPL.