As for logging the time, I am going to read up on logging P1S and P1 concurrently. Its not something I am very familiar with but I am assuming its not possible to log P1 and dual, as the check pilot is not FI qualified?
See
LASORS Section A Appendix B.
If by P1S you mean PIC U/S or P1 U/S that is only applicable in the case of a pilot undergoing any form of flight test with a JAA or CAA Authorised Examiner, or Co-pilot (on a multi-crew aeroplane.....) performing the duties of PIC under supervision of pilot-in-command.
If by 'dual' you mean P/UT then that is only applicable in the case of a pilot under instruction (by an FI) for the purpose of gaining a licence or rating, or for conversion to an aircraft type within an aircraft rating group or class.
You state that
The pilot to be checked already has a valid SEP class rating with differences sign off
therefore it would seem that the 'conversion' has already been completed.
If you are not an FI or FE maybe you could try Case N: Pilot acting as Safety Pilot = SNY
Whatever, there is only one PIC at any given time and that is for 'the checker' and 'the checked' to agree, and I would recommend that it be agreed beforehand.....
