the National Police Chiefs’ Council (NPCC) suggests police forces don’t prosecute until drivers exceed a margin of error of 10 per cent of the speed limit to take into account driver concentration, plus 2mph for speedometer error.
This means that most police forces will not prosecute until you’re driving at more than 46mph in a 40mph zone, for example, or 79mph in a 70mph zone. However, it should be noted that the guidance is exactly that, and that the decision over whether to give a driver a speeding ticket or not is entirely at the discretion of individual police forces and officers.
NPCC speed enforcement guidelines
Speed limit Min speed for a speeding ticket Min speed for prosecution
20mph 24mph 35mph
30mph 35mph 50mph
40mph 46mph 66mph
50mph 57mph 76mph
60mph 68mph 86mph
70mph 79mph 96mph
As an alternative to an FPN, most forces offer a speed awareness course. This is a course which takes place on one day, and as its name suggests, is intended to make participants more aware of their speed.
It’s offered only at the force’s discretion and cannot be requested.