British Secret Projects 3: Fighters from 1935-1950, by Tony Buttler, contains numerous built and unbuilt versions of the Meteor. These are:
P.147: Meteor with de Havilland Halford engines
P.148: Meteor with MetroVick engines
P.173: Trent Meteor
P.187: Meteor Mk.IV with Derwents
P.203: High-altitude variant of the Meteor, with Derwent 5. Came with a greater wingspan, which had squared off ends.
P.263: Meteor with delta wing, slab tail and Derwent 5s or 7s.
P.309: Eight-gun Meteor, fuselage of the F.8 with the wings of the NF.11, a truly formidable aircraft.
Regarding Maveric's question above (Post #44) about whether the experimental Meteors received Gloster's "P." designation system, it seems that some did carry one. Does anyone have any drawings or artwork of the aircraft mentioned above?