What warning phrase is famously heard on the London Underground?

The warning phrase famously heard on the London Underground is “Mind the gap.”

It tells passengers to take care when stepping across the space between a train doorway and the platform edge. The gap can be especially noticeable where a platform curves, because straight train carriages cannot align perfectly with the platform along the bend. Differences in train and platform height can also create a hazard.

London Underground introduced the phrase around 1968 as part of a recorded automated announcement. Recording technology was expensive and had limited storage capacity, so a short expression was practical for both announcements and platform markings. In British English, “mind” means pay attention to or be cautious about something; American English more often uses “watch your step.”

The phrase became a cultural symbol of London and later spread to transit systems around the world. Some systems use variants such as “Please mind the gap between the train and the platform” or “Watch the gap.” “Please mind the doors” is a different safety instruction, concerning closing doors rather than the platform-train space.