an honourable member in the 1950s seriously suggesting that vehicles should turn off their headlights when approaching each other, lest the drivers be dazzled ..
The law for a long time required that dipping the lights extinguished the offside headlight and dipped the nearside. This was usually achieved by pivotting the reflector, activated by an electromagnet.
When I bought my 1947 Triumph Roadster in 1966 it still had this mechanism, and shortly afterwards the double-dipping law was extended retrospectively to include all vehicles, including those originally only have single-dipping. At about the same time the requirement for two rear lights was also similarly retro-activated.
i believe these, and the windscreen washer requirement, are the only examples of such retrospective law-changing.
I recall a lively debate in the Roadster Club as to how to modify our vehicles. The silliest suggestion was to acquire a second pivotting reflector to replace the fixed one on the offside too - the drawback was that the mechanism, like that operating trafficators, was notoriously prone to sticking, and often only activated after passing over the next rut in the road. Two such headlights would not necessarily have dipped at the same time.
When I started driving in 1966 it was still considered gentlemanly to extinguish headlights when stopping behind another vehicle in a queue, or when passing pedestrians. In those days there were still two classes of motorist, the older ones having been driving before the war. The younger brasher post-war drivers threw aside all such considerations of politeness, so we now have today's universal free-for-all.