Pre requisite requirements for FI(A) rating
inc
completed at least 200 hrs of flight time of which at least 100 hours shall be as pilot-in-command if holding an ATPL(A) or CPL(A) or 150 hours as pilot-in-command if holding a PPL(A)
My gut feeling is that you can't use P1 u/s as anything that is u/s implies you are not PIC but best to double cx that one