But according to the Metropolitan Police, the rule is not a myth at all but in fact a real policing tactic used to determine speeding fine liability out on the roads.
A Freedom of Information Act request submitted to the Met in 2024 revealed that the 10% rule is a real thing, and set out how and why it’s in place.
Drivers will know that a speed limit of 30mph, or 50mph means that you cannot drive faster than the speed displayed in the red circle or you could get a speeding ticket, either from a camera or from a mobile camera unit.
“The Met observes the current NPCC guidelines which states that enforcement action should commence as soon as a speed that is at +10% +2mph. This is normally the minimum speed at which enforcement is undertaken in all speed limits.
Other police forces also use this 10% rule. In an FOI request submitted to West Yorkshire Police in August 2025, the force confirmed it employs this tactic, too.
It said: “The speed thresholds enforced by West Yorkshire Police are those set out in the guidance by the National Police Chiefs Council and are 10% + 2 mph.
“There are no variations on the speed thresholds. The speed of the road is what dictates the thresholds.”
Other forces confirmed to use the 10% + 2mph rule include Avon & Somerset Constabulary, West Mercia Police, Thames Valley Police, Gwent Police, Kent Police, South Wales Police. Suffolk Constabulary, North Wales Police, Police Scotland, Humberside Police and Essex Police.
However, it is important to note that the NPCC guidance is just that, guidance, and it is not actually law.
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Confused.com explains: “Speed camera tolerances are used at the discretion of the police to follow the rules around speeding, speed cameras, and the law.
Technically, the Association of Chief Police Officers (ACPO) allows a tolerance of 10% + 2 mph on speeding before taking punitive action. So they’re within their rights to punish drivers that break the speed limit by even just a few miles per hour.
“You can’t rely on these discretionary thresholds as a defence if you’re flagged for speeding. Going even 1 mile an hour over the speed limit counts as speeding, and you could be punished accordingly if caught.”
