No, part p is part of the building regulations. Obviously under some circumstances on some jobs you would need to comply with one or the other, or both, or none.
Because if you have done a PIR and it says you have tested everything but it turns out you missed half of it because the fixed wiring was on a plugtop and this then caused the house to burn down due to a fault you overlooked because you were being a pedant and ignoring the building regualtions then first of all you shouldn;t be doing PIR's and secondly someone wil want someone to blame, and you'll be top of the list.