Well in honesty I did say IMHO, yes I missed that part in point II
@Wilko - and agree with both you and
@Ian1981 on that.
I work on machinery to differing reg's and the reason for my take on this is safety under fault conditions, I see a big flaw in this regulation and I may raise it with the IET myself, but it would seem simply having the insulation value to the highest conductor would suffice, I would still consider the implications of the LV crossing over to the ELV and the potential risks associated with it if it were to occur, fusing alone isn't always a sufficient, like I said I said before, if DC is generated and isolated from the LV side in its generation then this could potentially create a accident waiting to happen.