Drivers caught doing 40mph in a 30mph zone can expect a fixed penalty notice of £100 and three penalty points on their licence, according to police guidance and motoring organisations.
The widely repeated claim that police will not fine drivers until they exceed the limit by 10% plus 2mph is correct in practice. Police forces generally follow National Police Chiefs’ Council (NPCC) guidelines, which state that enforcement action should begin at a speed of +10% plus 2mph. In a 30mph zone, that threshold is 35mph.
Discretion and strict liability
However, there is an important qualification. NPCC guidance also states that while tolerances exist, they do not replace police officers’ discretion in a given situation. Under UK law, speeding is a strict liability offence, meaning if a vehicle travels above the legal limit, the offence is complete. The police and Crown Prosecution Service do not need to prove intent or knowledge of speeding, and drivers have no legal right to a margin of error. So, theoretically, a driver could be fined for doing 31mph in a 30mph zone.
What the fine is for 40mph in a 30mph zone
The RAC explains that if you are caught driving 40mph in a 30mph zone, you will be prosecuted under the Band A rules, which means three penalty points will be added to your licence. You will also incur a fine, likely a fixed penalty notice of £100.
For more serious speeding offences or repeat offenders, fines can increase depending on income. Based on an annual income of £30,000, the following examples apply: driving at 40mph in a 30mph zone could lead to a fine of £288 (50% of weekly wage) and three points; driving 45mph could mean a fine of £577 (100% of weekly wage) and 4-6 points; and driving 51mph could mean a fine of £865 (150% of weekly wage) and 6 points.
Official enforcement guidance
Official guidance on the enforcement of speeding offences was issued in 2025 by the National Police Chiefs’ Council to provide transparency and consistency. The guidance includes a table showing that 35mph is generally the starting point for enforcement action in a 30mph zone. A National Speed Awareness Course can be offered for speeds between 35mph and 42mph. Alternatively, a fixed penalty notice of £100 and three points could be issued, but usually it is one or the other—if a driver is offered a course, they will not also be fined and given points.
