Doesn't surprise me Clarabel and Milly. I was discussing speeds with some professional drivers recently, articulated lorry drivers. All knew the speeds for their lorries correctly, but all thought that cars were restricted to 60 on dual carriageways.
Perhaps it is time for the authorities to re-educate people in some way. I reckon the majority of drivers do not know the national speed limits.
There is a speed camera on the A1 in north london on a dual section and I consistently see cars braking before it when they are already at 50, 20 mph below the limit.