Just been channel-hopping while I'm waiting for the wife and came across an
episode of DIY SOS. Billy the electrician was complaining that someone had
wired up some sockets in the kitchen by running the cable left-to-right
instead of up-and-down.

I thought you could run cable both vertically and horizontally, as long as
it is a straight run to an obvious socket/switch/whatever, eg, come down
from the ceiling to a socket, then say out a metre to the right for another
socket, and then take the return leg back to the first socket box and back
up the chase to the ceiling again?