This is part of a total re-wire to new 17th ed. regs. & everything with RCD protection.
The sparky told me that he couldn`t take a horizontal run from one socket outlet to another ( only 18" apart ). He would take a vertical to the ceiling void go across then down to the finished socket position (on every socket).
I didn`t question his method but could not find this info. in the 17th ed. regs. book or the on-site guide book.
In the ECA guide to the Wiring Regulations 17th edition by Darrell Locke figure D 5.1 page 109 (section D) it shows cable safe zones. This page shows a horizontal safe zone band from a socket to 150mm corner wall area with verticals. Is this info. deceiving as it seems you can put sockets along this horizontal band (but can you run cables in this zone).