Do you have an electric drill or other similar tools which are intended to be hand-held?This holder is metal but is isolated by a plastic sleeve, however my issue is that supposing the wires that are connected to the holder were to become detached or are not fitted correctly at manufacture or the flex clamp screw had been overtightened (there is no way to check or tighten the wiring inside the holder, it's all done at the factory prior to assembly.) They could touch the metal outer skin of the bulb holder.
Add to this the fact that there is a rotating on/off switch on the holder meaning that you would be touching the holder each time you turn the light on or off.
Class 2 is considered a suitable, indeed superior, method of protection and the metal parts must not be earthed.Is this normal construction or should all the metal parts be earthed (cpc?)?
Earthing is not a good thing in itself. It is a necessary evil when the only method of protection by disconnecting the supply before you get a shock.