You presumably mean 12V which is extra-low voltage - normal mains is low voltage (not high voltage).To satisfy my curiosity, do you or anybody else have any opinion on why the authorities thought the positioning of low voltage fittings was their concern?
Yes, I meant elv as did Welshjeff1000. Something like this http://www.screwfix.com/p/lap-fixed-white-12v-low-voltage-bathroom-downlights-pack-of-3/34883 Complete kits can be bought.
The positioning of them is not the issue.
Not within a zone. But in the sense that they are concerned when things move from outside to within zones 1 & 2.
Except for "preassembled lighting set bearing the CE marking referred to in regulation 9 of the Electrical Equipment (Safety) Regulations 1994(1)"
they are classed as a special installation and are notifiable.
I would think the reason is because the low voltage results in high current, leading to circuit design issues.
CE not known here but although it requires the parts to be plugged together the cables are preassembled, so there are no design/workmanship issues.