Fair enough, but the point being made was that if any of the wiring in the lighting circuit (including that to switches etc.) was 'buried' <50mm below the surface of the plasterboard, then the regulations would require the circuit to have RCD (or RCBO) protection (and also routed in the prescribed 'safe zones'). If the wiring were entirely on the surface, and visible, there would be no such requirements.... Roof is boarded and covered with two layers of felt, insulation inside and also plasterboarded. Its very snug and dry. ... The light are fluorescents that are all internal to the workshop, there is no external lighting on the workshop light circuit which is wired in 1.5mm twin and earth, all fittings are correctly earthed.
Kind Regards, John
Ah! Of course. No all the workshop wiring is surface mounted. At the back of the workbenches, and in some other areas, it is in plastic trunking.