My house is not particularly well specc'ed for electrics; although we do
have fairly modern RCD-protected CU and reasonably new wiring, we don't
have adequate circuits and it's likely that one day I'll want to sort it
out and add a few ring mains when the opportunity permits (eg, when one
day that new kitchen comes to the top of the round tuit list...).

Anyway, shortly due to arrive at the top of said list is the
redecorating of the hall/stairs/landing (urgh). Now, the CU lives in a
low cupboard in the hall, and all the cables running from it are buried
in the brick/plaster wall above it, travelling up to the ceiling. Can't
see any scope for adding in any new cables without serious wall surgery.

So it occurs me that *now* would be a good time to bury some form of
conduit in the wall, separate but adjacent to the existing cables, to
enable me to run new cables at some time in the future. It would
clearly need to be a pretty large cavity to be worthwhile (I might want
to put several ring mains down there, and they'd have to be pulled
through which would be awkward). "Large" to me implies fairly deeply
buried, to ensure the overlying plaster is rigid enough not to crack.

While I'm mulling this over in my head, I'm just wondering if anyone's
tried something similar and have any tips for suitable conduit, methods etc?

Thanks
David