You can get class II metal fittings, but there is normally nylon sleeves inside the pipes which the wires go through, and when testing we use some thing like 2500 volt to ensure the insulation is sound.
For an earthed system 500 volt is considered enough.
Pre 1966 lights were not earthed, the rules were changed because people were getting shocks off the lights, so houses wired before 1966 and lights designed for those houses did not have earth wires, the rules say you can continue using pre 1966 stuff, but any new has to conform with new standards, since you can't type test a single fitting, you can't really use any old fittings unless you fit an earth.
It is rather a debatable point, rules say any class II item needs to be marked class II, well with screw bulbs it is clear they are class II there can only be two connections, centre pin is line and screw is neutral, but with bayonet bulbs the standard BA22d the case could be earthed, so in theory every BA22d bulb should have the double square marking on it to show it is class II or the shell of the holder should be earthed.
In practice I have never seen a BA22d bulb marked as class II, it is a historical thing, no one has ever bothered, as until the energy saving bulb there was never a need for an earth as near impossible for a tungsten bulb to make the shell live.
However any scheme member electrician has to follow BS7671 so if they did an electrical installation condition report likely not earth on lights would mean unsatisfactory label, it would be up to the electrician to decide if he considers it as a likely danger or not.
With an owner occupied house likely one could get away with it, with a rented house, likely next inspection it would be changed and the tenant charged for the work.
Until recently there was no law about inspecting electrics, but starting in Scotland laws now protect tenants, and so things which have been done by tenants in the pass and ignored by the owners, now are being picked up, idea was make it safer for tenant, result is less houses for rent.
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