speed trap stealth tax !

The news today is that there will be a grading of speeding offences caught via speed traps.
At least that's what the newspapers trumpet.
In reality , there will be a £20 fine for people who travel at up to 39mph in a 30mph zone with ONLY 2 points on your licence [you need 12 to lose your driving licence]. Sounds great uh ?
As I understand, the speed trap system is set up as follows :
30 mph - fine. Then there is a 10% allowance for the speedometer being faulty/tyres not inflated properly, then there is a further 10% allowance for the camera [not the doppler] and its associated white lines for the photographic evidence, then finally there is a nominal x for 'luck'.
Thus cameras in a 30mph zone are set to click at about 37-39mph.
Hence we have another stealth tax coming in , but portrayed as a 'present' to the victims.
I find it very hard to keep under 30mph except in built up areas, so its gonna clobber me quite badly, and I suspect lots of others.
Last year apparently those metal monsters caught 3 million vehicles and I reckon this new measure will double it to 6 million. That would make 10% of the population of the UK being fined each year, and assuming there is 1 car/2 people in the UK, thats a fifth !

Something is seriously wrong with this system