Thanks for (most of) the comments.
Follow on question:
I keep reading "The air flow over the swept wing is at 90 degrees / perpendicular to the leading edge, so the air is actually veering towards the fuselage, and is tricked into thinking the aircraft is flying slower, and therefore the airflow over the wing is not reaching supersonic range, and having associated shockwaves / drag."
OK, but what "law of physics" stops the air from just flowing STRAIGHT from front to back over the SWEPT wing??? Why does the sweep reroute it at 90 degrees? At what sweep angle does effect collapse??????? Surely a (rediculous angle for argument's sake) 80 degree swept wing wont divert air at 90 degrees to leading edge? Airflow would nearly be sideways???
I hope somebody can see my confusion and give me a "eureka" moment.
Thanks in advance.