On 9 June 1952, it was decided that there would be a second phase of prototypes built to develop the aircraft towards achieving ; these were designated "P.1B" while the initial three prototypes were retroactively reclassified as "P.1A". P.1B was a significant improvement on P.1A. While it was similar in aerodynamics, structure and control systems, it incorporated extensive alterations to the forward fuselage, reheated Rolls Royce Avon R24R engines, a conical centre body inlet cone, variable nozzle reheat and provision for weapons systems integrated with the ADC and AI.23 radar. Three P1B prototypes were built, assigned serials XA847, XA853 and XA856