It makes no difference what the Police think. The maximum speed permitted by law on our roads is 70mph. If it were permissible to travel at 80 mph then the speed limits would show 80mph.
If you were driving in a 30 zone and doing 35 and you struck a child then there would be the much greater likelihood that that child would die. As the TV advert says - IT'S 30 FOR A REASON.
If a pedestrian is struck at 30 mph then 80% will live.
If a pedestrian is stuck at 40 mph - the 80% of them will die.
So where does your 10% rule fit in?
In many cities the limit is to be reduced to 20mph so the authorities clearly disagree with your 10% rule.
Joe. It's NOT my rule. Most of the Constabularies around the country have adopted this "rule" for want of a better word.
They have decided to allow 10% for inaccuracies of speedos and their variation between vehicles.
If councils do reduce inner city limits to 20mph, then the same "rule" will be applied, ie anything over 24mph in a 20 zone will attract attention.
Of course, the signs don't have an asterix next to the number with a disclaimer at the bottom which says,
"MAXIMUM SPEED PERMITTED SUBJECT TO AN ADDITIONAL 10% FOR SPEEDOMETER INACCURACIES PLUS A FURTHER 2 MPH."
But, like it or not, that is how most speed limits are interpreted.