Ah, well, how many people do anything 'properly' nowadays when it is hidden from view and they are not being watched. Not all, I suspect.
But, for those who live and die by the regulations, it appears to be allowable. If one considers 'safety' to be paramount, whatever that is, then surely having a cable behind four inches of brick has to have safety advantages over having a cable behind 12mm of plaster board and a layer of wallpaper. I suppose like all things, it depends.
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