Flybiker, although I agree with you, you have failed to mention any British contribution to breaking the "Sound Barrier" and only mentioned US X planes and P51.
In WW2 and shortly thereafter the British had some high speed piston-engined planes (e.g. Spitfire, Mosquito, Hornet etc) and (from 1944) jet planes, all of which (with their superb pilots and test pilots) contributed knowledge and experience towards supersonic flight. One of the most important contributions was by Denis Bancroft inventing the all-moving tail plane for the Miles M52.