The P.85 was Boulton Paul's tender to Specification O.30/35 for the naval turret fighter (eventually won by the the Blackburn Roc). It had a deeper fuselage and leading edge slats, for the lower landing speeds required of carrier aircraft. The engine would be either a Bristol Hercules radial or the Merlin.
The P.85B, Merlin-powered version, with side view of the P.85A Hercules version:
The P.85 floatplane, Hercules-powered:
Personally, I plan to do a carrier based Sea-Defiant someday. Mine will be a lot simpler though with a standard Defiant with added tail hook and folding outer wings (which will include a pair of MGs).