Technically everyone, but it is van and car drivers who must be specifically careful.
What do the regulations say?
Drivers must be qualified for the combined weight of the vehicle and trailer. Furthermore, higher weights may take the vehicle within scope of O-licensing, tachographs and additional drivers’ hours rules.
Speed limits are lower.
For further details, go to: commercialfleet.org/towing-laws
Who enforces it?
DVSA and road traffic police.
Dependent upon the infringement (for instance, if a licensing, drivers’ hours or dangerous load offence).