Hmm, that's interesting. My house is a 30's place, but the wiring
looks reasonably modern to me (circuit breakers not fuses, etc.) Just
how old would wiring be for you to expect lighting circuits to not be
earthed?

I can see the ceiling rose has been moved in the room in question, so
another possibility is that a new cable was installed for the move,
and earth omitted at that point. I'll investigate more closely.

Thanks..
Matt

Dear me, no. The first point is that if your wiring is of such an age that
the lighting circuits have no earth, then you ought to be thinking in terms
of a complete re-wire before too long.