Andy Champ wrote:

I don't see the relevance of the age.

If the cabling is pre-1984 2.5 mm^2 T&E - quite possible in view of the
older BS 3871 type MCB mentioned - then the earth conductors acting as
neutral will only be 1 mm^2 and could be liable to serious overheating
under overload, not protected by the MCB. With later 2.5 T&E the
problem won't be quite so bad.

--
Andy