I'm no lawyer and certainly don't want to start a legal argument, but doesn't the discretion refer to admin? As I said I'm fortunate in that I haven't need to test the application of the guidelines (and with most of us I suspect that it is just good fortune!)
The guidance was updated in April 2010, prior to that one of the footnotes said:
3 ACPO bottom level threshold – ACPO set a limit below which speed offences should not be prosecuted so as to allow for equipment inaccuracy, speedometer inaccuracy and human error interpreting a speed indication by dial. Prosecutions below this level should be undertaken by way of careless driving or other offence, not speed offence alone.
Still puzzled in Stoke!
