Welcome to Flyertalk obbiie, and a very warm welcome to the BA board corner of Flyertalk! I hope you stick around and partake in our discussions here!

P fare is either a redemption or, usually a sale or discounted ticket. It is perhaps used for when there was a WT+ sale, cheap upgrades to WT+, etc as well as Avios redemptions. It is usually to prevent further upgrades into CW.

P will give you the full WT+ tier points and miles as you have paid for it (either outright or as an upgrade from WT+).

Otherwise, if it was an Avios upgrade/redemption, then of course no miles or tier points will be awarded.