1970s house. Breezeblock + plaster inner walls.
Whilst taking the tiles off in the kitchen, near the fuse box, a patch
of plaster came away revealing what seemed to be thin wood(?!) in the
wall. I also saw a grey cable -- which I take to be one of the ring
main circuits.

* I patched the wall up and have marked the location of the grey cable
with an arrow scratched on the wall. Is there a standard symbol for
marking the location of electrical mains cables (E, perhaps?)

* Is it possible someone used wooden trunking for the electric cables
prior to plastering?

Bruce