Under EASA rules, if the instructor does not have a medical they cannot act as an instructor, so you could only be PIC. If you are flying Dual i.e. the Instructor is ecxercising the privileges of an Instructor Crertificate, then you cannot be PIC and the hours are not acceptable towards your 6 hours PIC. If you don't have the hours, do a Prof Check, the hour with an Instructor will not count either with a FAA CFI.