Do you have an image of the base of the projectile?
Have you disassembled the 'fuze'?
A "Fuze, Percussion, Q.F., 1Pr." should have a flash hole in the bottom of the fuze, from the above image it would appear this is not present. The Day Tracer Projectile, Mk I used "Plug, Fuze Hole, Q.F., 1 Pr" from the plate, one assumes this was machined from solid. I suspect that this is a 'Plug' fabricated from fuze components. The 'P' in this instance, is to signify that it is a 'Plug' and not a 'Fuze.'
TimG