the difference between 'code minimum' and 'trade practice.'
Or what one might consider to be good practice even if not always common trade practice.
There's no specific ban here on using the British equivalent of NM cable in light commercial applications, although in many places where surface run neatness would dictate the use of plastic trunking.
In many cases though, in my opinion the amount of work involved in cutting and fitting rectangular PVC trunking and then laying NM cables exceeeds that needed to just run PVC conduit and pull singles through it. The conduit gives a much neater result anyway.
See
this thread for an example.
