The Metropolitan Police enforcement threshold for speed cameras is 10% plus 2mph. That's not anecdotal advice from a mate down the pub. It's a confirmed policy stated in official Freedom of Information responses published on the Met's website.
According to the Met's FOI disclosure, the force follows National Police Chiefs' Council guidelines, which state that enforcement action should commence at speeds of 10% plus 2mph above the posted limit. In a 30mph zone, that means cameras typically don't activate unless a vehicle passes at 35mph or higher. On a 70mph motorway, enforcement begins at 79mph.
The threshold exists as a margin for error. Speedometers aren't perfectly accurate. GPS units can be off by a mile or two per hour. Speed camera technology itself has tolerances. The 10% plus 2mph buffer accounts for these variables to ensure that drivers ticketed for speeding were genuinely exceeding the limit, not caught by instrument variance.
A Confused.com investigation contacted 45 UK police forces in February 2023. Of the 39 that responded, 26 shared information about their speed camera activation thresholds. Most confirmed they use the 10% plus 2mph standard in line with NPCC guidance.
Forces confirmed to operate at 10% plus 2mph 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. West Yorkshire Police confirmed the same threshold in an FOI response from August 2025, stating "the speed thresholds enforced by West Yorkshire Police are those set out in the guidance by the National Police Chiefs Council and are 10% plus 2 mph."
But the rule has changed recently. Until May 2019, the Metropolitan Police used a more lenient threshold of 10% plus 3mph. RAC reporting notes the change was never publicly announced, and many drivers remained unaware their margin for error had shrunk by 1mph. Under the old threshold, drivers could reach 36mph in a 30mph zone before facing prosecution. The current threshold drops that to 35mph.
Lancashire Police also previously operated at 10% plus 3mph but has since tightened enforcement to match NPCC guidelines, according to RAC research.
The stricter enforcement has consequences. According to a This Is Money report cited by the RAC, the Met's threshold change could result in more than 347,000 additional prosecutions between January and June of the year following implementation. The difference between 35mph and 36mph in a 30mph zone might seem trivial, but at scale, it represents tens of thousands of speeding tickets.
Police stress that the threshold is discretionary, not automatic. The Met's FOI response explicitly states that "NPCC guidance also states that whilst tolerances exist, they do not and cannot replace police officers' discretion." Officers can still prosecute drivers traveling just 1mph over the limit if circumstances warrant it. The 10% plus 2mph figure represents the minimum speed at which enforcement typically occurs, not a legal entitlement to exceed the limit.
The Metropolitan Police told Confused.com that "speed camera tolerances are discretionary. That means police can still prosecute you even if you go just 1 mph over the speed limit. And a speeding conviction comes with a fine, points on your licence and higher future car insurance costs. It's not worth it. You should always drive at a speed that's legal, safe and appropriate for the road."
Different camera types may apply thresholds differently. Average speed cameras monitor velocity over several miles rather than at a single point, theoretically making them more accurate and potentially less tolerant of marginal speeding. Mobile speed camera vans operated by officers also rely on individual discretion rather than automated thresholds.
Essex Police confirmed in an FOI response that while they follow ACPO guidance allowing speeds of 10% plus 2mph to 9mph above the limit for speed awareness course eligibility, they "use slightly different speed enforcement guidelines and as suggested these are guidelines and a decision is made by the officer as to what to prosecute."
The practical takeaway is straightforward. The 10% plus 2mph threshold is real. Multiple police forces confirmed it through FOI requests. It's based on official NPCC guidance designed to account for measurement tolerances and ensure fair enforcement. But it's not a loophole, and it's not guaranteed. Officers retain discretion to prosecute at any speed above the limit. Speed cameras are calibrated to extremely tight tolerances, and relying on a 2mph buffer while watching your speedometer instead of the road defeats the entire purpose of speed limits.
Drivers who treat 35mph as the new 30mph limit because they read about enforcement thresholds online are gambling with penalty points, fines, and insurance premiums. The threshold exists to protect drivers from unfair prosecution due to instrument error, not to provide a legal margin for intentional speeding. The speed limit remains the speed limit, and anyone exceeding it is technically breaking the law regardless of enforcement practices.
Police have been clear about this. The Met, West Yorkshire Police, and multiple other forces all stated in FOI responses that drivers should stick to the posted limit. The 10% plus 2mph rule is an enforcement guideline, not permission to speed. Knowing it exists doesn't change what drivers should do. It just confirms what happens when they don't.