You are. I can't think of any situation when you're giving instruction, where you wouldn't be the PiC (unless you are renewing your own instructor rating with an FI examiner of course). The relevant CAA white paper for PPL renewals (forget the number now) quite clearly says that a PPL holder wishing to renew their C of E, must in addition to their 12 hours in the preceding 12 months etc etc, have logged one hour's DUAL with an FI.