I think it’s the dog light that has to be on the correct side isn’t it?
That would seem to make sense, but I just found this in a fairly old forum (not this one) about taking RHD cars onto the continental mainland:
One red coloured rear fog lamp must be fitted to the centre or offside of vehicles first used from 1st April 1980. Additional rear fog lamps or rear fog lamps fitted to vehicles first used before this date are not testable.
If that's true, a pre-April '80 car can either have no fog lamp, or one on the 'wrong' side. Personally, given the size of the 126 and the way some folks drive in fog, I think I'd want to be as bright as possible in poor visibility - at least 4 fog lights, one on each corner, plus three red lights in the centre of the roof, US truck style !!