In the United Kingdom, what does a circular sign with a black diagonal stripe mean?

In the United Kingdom, a circular sign with a black diagonal stripe means the national speed limit applies.

The sign is a white circle crossed by a single black diagonal stripe. It tells drivers that a previously posted lower limit has ended and that the applicable national limit now governs, subject to the type of road and vehicle. It does not mean that every road has the same maximum speed.

For cars and motorcycles in Great Britain, the national limits are commonly 30 mph in built-up areas unless signs say otherwise, 60 mph on single carriageways, and 70 mph on dual carriageways and motorways. Different limits can apply to other vehicle classes.

The sign is often confused with signs ending local restrictions. Its meaning is specifically tied to the national speed-limit rules, so drivers must still identify the road category and their vehicle type.