A couple more What-Ifs, not post-war jets this time but WW2 era...
The Hawker P.1030 designed in 1943 with the RR Eagle engine, estimated to achieve 509mph at 20,000ft. Armed with 4x20mm cannon. This was about the end of the line of Camm's piston fighters and of course the earlier Tempest and Sea Fury were the last to be built.
The Supermarine Type 327, designed in 1939 as a twin-engined fighter with two Merlin engines, six 20mm cannon in the wing roots and a tricycle undercarriage. Focus on Spitfire production and the decision to arm the new Hawker Typhoon with cannons stopped the project.