Perhaps everyone should do a speed and safe driving course every 5 years, if only to keep up with the ever changing rules!
The comment SFG made about rigid enforcement is a view held by a minority of Police Force heads, but is not (yet) policy set by the Association of Chief Police Officers.
Their policy remans that the threshold for a NIP is the posted limit plus 10% +1mph.
There is an equally vehement group of Chief Police Officers who want the limit on Motorways and other roads built to Motorway standard to be raised to 80mph. Again, this is the view of a minority.
Given the inherent over reading of most car speedometers this means that to get a ticket on a motorway for exceeding the limit most cars would be showing 80 on the speedo.