Around here (we are just off the M25) folks have had tickets at 53mph in a 50 enforced zone. I guess around the variable sections they really mean 50 when they say 50 etc, and it's by and large all averages now. The section from clacket lane through to the M23 exit for example has 3 average speed sections back to back.
And they are pretty aggressive at the Dartford crossing north bound. But southbound over the bridge seem to be very lax (?!)...
I got flashed by a variable speed camera on the m25 when they said 40mph and I was doing 43, never got a ticket but that may have been ‘cos I was driving an ambulance!
I think the 10% +2 margin has probably gone these days.
The problem on the M25 is they keep sending the limit up and down, and for no apparent reason, especially at night. You can be trundling along at 70, then there’s a gantry saying 40, then the next says 60, then 40 etc etc. There has been a suggestion this is done deliberately as a revenue raiser, along with reducing the tolerance.
It is worth noting that, contrary to the propaganda, the introduction of speed cameras made no identifiable change to the death rate on our roads for the 10 years after their introduction. The articles suggesting they did tend to look selectively at certain years to prove their point but if you look at the overall figure, they made no difference. The single biggest factor in reducing road deaths has been vehicle design.
It is also worth noting that speed is rarely the principal causative factor in accidents, especially on motorways, which are statistically our safest roads. Where speed is a causative factor it is not speed itself, but inappropriate speed, that may even be below the speed limit.