An FPN, or fixed penalty notice, is an out-of-court fine issued by police or another enforcement body for a minor offence. Paying it settles the matter without a court hearing, and a motoring FPN can carry penalty points on the licence.
In one line: An FPN is a police-issued fixed fine that settles a minor offence out of court, sometimes with penalty points attached.
How an FPN works
FPNs cover offences such as speeding, using a phone while driving or not wearing a seatbelt. Accepting one is a way to dispose of the matter without prosecution, but it is still a criminal sanction recorded against the driver.
The minimum motoring FPN for speeding is 100 GBP plus 3 penalty points (GOV.UK). For example, a driver caught slightly over the limit who accepts the FPN pays 100 GBP, gains 3 points that stay relevant for totting up over three years, and avoids a court summons.
If the recipient disputes the offence, the FPN can be declined, sending the case to a magistrates' court where the penalty, including the fine and points, may be higher if convicted.
FPN vs PCN
An FPN is a criminal penalty from police that can add licence points; a PCN is a civil parking or traffic charge that cannot. The two are issued under different laws and resolved through entirely different appeal systems.
Conditional offers of a fixed penalty for speeding often arrive with the option of a speed awareness course instead, which a parking PCN never offers.
Primary source: GOV.UK: Speeding penalties