Well, it's been longer than expected, but I've finally got my junction
box sorted out. Those of you with good memories will remember that I
posted this:

https://goo.gl/photos/UCcAYGiRfjAbnWhy5

After re-arranging the earths into some sort of sanity:
https://goo.gl/photos/jRETkargbvyBS8D6A
Opening the box revealed this mess:
https://goo.gl/photos/goY21SS2Q54YuwLb7

So, after a lot of checking I discovered that half the cables weren't
connected to anything. I also found another junction box not passing
through the earth - not so bad when feeding a transformer for 12V
lights, but I wanted to fit mains ones. I also found another ceiling
rose being used as a junction box, and a 13A socket fed from the
lighting circuit - though on a shelf, so it looks like it was intended
for a light. No label, though.

Having got rid of the redundent cables, removed the surplus junction
boxes, and replaced both the dining room and bathroom lights, it now
looks like this:

https://goo.gl/photos/2K4RkHhEYVNpEtUj7

And with the lids on:

https://goo.gl/photos/XDz6dH4qX8uAGnZr8

Everything labelled, no redundant cables, the earths connected to proper
terminals (and sleeved). There's still one flaw - there's no sign of
equipotential bonding in the bathroom. There's an RCD on the shower
circuit, though, and the shock risk from the lights should be pretty low
since they're out of reach without standing on something, so it can wait
for now.

Now to find out what's in the other loft...

Mike