Nice contribution Molgrips. Really useful.
I know that not everyone is a professional driver but as a professional driver, driving is the one area where I do NOT have to have refresher training etc.
As it happens, I work for an outfit that do recognise additional training and every 2 years, I undergo a refresher. Yes, my driving is effected by having someone sat with – just the same as everyone who did their test the first time BUT ….. I always pick up something new everytime AND the refresher training has CHANGED my driving habits and (in my opinion) I am a better driver for it. I can still charge up the M4 at 100mph+ (but I don't) but the times when I would charge up the M4 would be better calculated as to when such a speed would be appropriate for the conditions.
What really gets me is that those that say "its a limit don't exceed it" don't seem to accept that it can be equally dangerous to drive at a speed that is less than the limit. This is where experience and training comes into it by the driver being able to assess an appropriate speed.
There is no god-given right to drive and having to undergo regular training in order to keep up a licence would (in my opinion) have far more greater positive impact on road incidents than installing cameras.
But before I end on a digression from the OP, I am keen to see what effect installing the cameras AND increasing the limit will have. Maybe it will be the start of increasing limits in other areas?