"Chasing in" wiring in a wall, an engineer has refused to conceal some new wiring, and made it surface mounted because he says Horizontal chasing in of wiring is not allowed, but it would have be OK for vertical wiring, is this correct or is he just trying it on to save work! (although I can see a logic behind the statement)
The reason you don't chase in electrical wiring 'horizontally' is that once it is done there is no clue that it's there and subsequently someone could inadvertently cut through the cable. It's ok to do it vertically as anyone would see the device/outlet at the bottom and know that the cable would run directly up from the device.
The wiring regulations of the UK (16th edition) states that you can not conceal wiring horizontally. A posible solution is to take the wiring vertiaclly up and in to the ceiling, then across and back down again. All would then be concealed, but it is more work and cost.