I think it is becoming more and more difficult to be certain what the speed limit as at all times, but you don't.That doesn't prove anything other than the number of speeding offences going up. It doesn't include any data relating to the reason for the offence. Some will of course be people not knowing what the speed limit is, and others will be people knowing what the limit is and choosing to ignore it assuming they won't get caught. There is also no information about the number of cameras in use.
We'll just have to agree to disagree then.