I don’t mean the flashing orange signs,
You won’t get done on those, they’re advisory not mandatory.
If they are in a red ring they are mandatory.
EDIT:
261
You MUST NOT exceed 70 mph (112 km/h), or the maximum speed limit permitted for your vehicle (see Rule 124). If a lower speed limit is in force, either permanently or temporarily, at road works for example, you MUST NOT exceed the lower limit. On some motorways, mandatory motorway signals (which display the speed within a red ring) are used to vary the maximum speed limit to improve traffic flow. You MUST NOT exceed this speed limit.