P4 Royal Mail Stamp Booklet vendor   The P4 is a battery operated Stamp Book issuing machine developed for the Post Office, with Hillday designing and manufacturing the working part of the machines with the Post Office designing the very attractive door. The whole machine is designed for outdoor use on the side of pillar boxes and through Post Office walls. With its predecessors, the B52, P1, and P3 , Hillday have supplied some 2000 of this range of battery operated booklet machines.