I have been informed that both the upstairs and downstairs lighting
circuits are not earthed, the property was built in 1961.

Could people answer on what would the estimated cost would be to
replace these circuits and what would entail please. I see this as an

Don't bother if it is PVC and you have no non-double insulated metallic
fittings. If you are ever redecorating a room, you could then run earthed
cables for that room then, but the disruption of rewiring lighting circuits
to add earths is all out of proportion to any safety benefit you will
obtain, which is pretty well a fat zero if you have plastic or double
insulated metallic fittings.

Christian.