Capping doesn't provide sufficient mechanical protection for you to run cables outside the zones and less than 50mm deep anyway...
If mechanical protection is required (burying outside the zones) and galvanised steel conduit is used, does it need to be earthed, or is that only for a full run of conduit from box to box?
I ask because I want to mount light switches and a thermostat in the end of a brick wall (as distinct from the faces of the wall) in my hallway, which doesn't form part of a corner (it's just the continuation of a wall in my living room past the l/r door). I was planning to use capping for the runs of cable within the zones and then go into conduit for the remainder of the runs which are outside the zones into the back boxes.