Ian,
Over here, it is standard trade practice to use fibreglass sleeving over the phase and neutral wires that actually make contact with the bulb in light fittings.
When I say "standard practice", I mean that only the clued-up, responsible electricians are doing this.
As an Inspector, I've failed at least 2-3 installs where this has not happened.
As a Fire Officer, one of the most annoying calls to attend, is a roof fire started by an over-lamped (sometimes 150W+) fitting with the cover removed, the top of the bulb is always the hottest part (when the bulb is mounted base upwards), that heat is borne by the light socket, the terminals and ultimately the wiring attached to it.
Using fibreglass sleeving minimises the risk of a short circuit in the roof or around timber that the fitting is screwed to.
