Crikey, that’s a lot of chasing for a light switch! This man must enjoy hard work.
The runs by the door appear to be more than 150mm from the corners so are (just) out of the regulation zones. The horizontal run is compliant.
BUT contrary to what others have said above, IF the circuit is 30mA RCD protected (OP please check if there’s a little test button on the breaker for this circuit in the consumer unit) my understanding is that wiring can be shallow, and unprotected, so it’s not a major departure overall.
I checked Section 522 in detail when I rewired my own house, and wanted to keep some electrically sound, but badly-run existing lighting drops, which were certainly less than 50mm deep. My installation now has 6A/30mA RCBOs on all the lighting circuits. I’m absolutely sure it complies.
My understanding is that new cable installs:
1. MUST be in the ‘safe zones’ but,
2. If the wires are shallow, have no mechanical protection, or are in a partition with metallic structure (regardless of cable depth), that’s fine, but the circuit must be RCD protected, that’s all.
Clearly one can’t be expected to cut a horizontal chase over 50mm deep into, say, a single brick load-bearing wall without the immediate danger not being electrical…
ps That said, I think it looks a bit of a pig’s ear, and it's not how I’d have done it, but I’m not convinced it’s grossly non-compliant.
Maybe there was an absolute client prohibition on disturbing ceilings or floors? Or it’s a flat with concrete ceilings and a solid floor?