The bit about the Me 262 has reminded me; I vaguely remember a story (Aeroplane Monthly?) about the air speed record attempts in a Meteor just after WW2. I think it said that during development flying of the aircraft selected for the attempt, they encountered mach buffet whilst flying over the Bristol Channel (presumably operating from Brockworth or Moreton Valence). No claim for exceeding M1 was ever made, but you wonder how close they got.