It is not a safety defect of the vehicle. It's operation is not safety predudicted. It curtails the operation/use of the vehicle in certain circumstances, it will be the driver not the vehicle that commits an offence. And it " may" TBC, make all Grenadiers on the UK not eligible to be driven on the public highway when they reach there 3rd birthday.
I read the uk Road Traffic Act 1988 which does explicitly state that no construction of vehicles may be done without confirming to lighting regulations.
And the act is very specific on this, as is the supporting vehicle lighting law.
surely there must be a legal instrument and supporting process for reporting manufacturing compliance violations against the statue to the regulatory agency?
Btw, this is not at all how the US does it. The law confers powers to nhtsa to enact rules for safety. Vehicles manufactured for sale must conform to these safety rules. But the rules are not in the law itself, it would be much to slow to leave that to law making, its done in rule making which also must follow a specific process across agencies.
Once sold, it moves to traffic enforcement and state laws. They typically incorporate rules from nhtsa into their law making. Uk kind of makes all of this into one law that spans both making of a vehicle with operation and maintenance of a vehicle.
Not stating that one is better than the other, just different because of states vs federal in the US. It makes nhtsa a single point of enforcement for safety with manufacturers and states a single point of enforcement for maintenance and modifications with owners.
Of course nothing is a simple as that, we also have two other laws,
Energy Policy and Conservation Act of 1975, the Energy Independence and Security Act of 2007, which is the foundation for fuel emissions or the cafe rules for car manufacturers that nhtsa also administers. this collides a bit with environmental protection agency and in particular with California's air resources agency who also make rules in these areas. But for vehicle safety nhtsa is it.