I sympathize with the OP but I very much doubt this statement:
driving at indicated 50mph as was everyone else
Every other socket on there seems to scream along in the middle and RH lane and then they heave on the anchors when they sight a yellow gantry.
Obviously this erratic twattery must “Average out” to ~50mph somehow or else they’d have all calmed down by now? But I can’t help wondering what these tools understanding of the word “Average” actually is…
I stick to what my speedo says as it seems to tally pretty closely to my Sat-Nav, and I just use the same lane discipline as everywhere else, if someone wants to go faster I’ll do my best not to hold them up but if I can’t pull in to the LH lane I’m not toeing it over the speed limit just to keep some arse in a van happy, and I’ll assume those cameras actually work until told otherwise…
Anyway email his boss, unless they catch a bollocking of some sort some people just don’t learn, and it sounds like you did nothing wrong OP.