This 2-door sports car used an updated version of the Wolseley Motors-designed and made overhead camshaft, crossflow engine, used in the 1928 Morris Minor and previously fitted in the J-type Midget of 1932 to 1934, driving the rear wheels through a four-speed non-synchromesh gearbox.

The chassis was a strengthened and slightly longer version of that used in the J-type with suspension by half-elliptic springs all round with rigid front and rear axles.

Whereas J, K and L-type MGs differentiated between versions with the use of numbers, with 1 indicating a four-seater (i.e., J1) and 2 a two-seater (i.e., J2), this was not the case with the P-type (or its six-cylinder sister, the N-type Magnette), and there is no clue to the type in the name.

The first PA used an 847 cc (51.7 cu in) engine similar to the J-Type's, now with a 3-bearing crankshaft, improved camshaft, and twin OM-model SU carburettors.

Externally very similar to the PA, the main differences in the PB are a vertically slatted radiator grille in place of a honeycomb, and the design and material of the standard dashboard.