This afternoon, I have been replacing a light fitting in a storage area
that got broke last week.

I took off the old fitting, there was a green sleeved wire going to the
light fittings earth point (the fitting was all plastic). A black wire
going to one side of the bulb holder, a red going to the other side of
the holder (this cable also carried the earth I mentioned above) and a
black wire that did not look as if it had been connected to anything.

I fitted the new light, only to find that the rest of the downstairs
lights were not working. After a bit of head scratching I decided that
the two black wires must be neutrals and joined them together. The house
lights came back on.

Is it normal to loop neutral cables to light fittings? By the way, this
is the light fitting closest to the fuse box.

Dave