Terminal blocks inside a metal double insulated ceiling light

[ban-all-sheds]

Easy enough to check.

But if you don't want to cut one of the conductors, ask them again if they are confident enough of their assertion to send you a short piece of the wire to examine, and tell them that if not you will ask Trading Standards to look into bringing criminal proceedings against them.

 

[SimonH2]

Not only that, but if the cores really are DI, why over-sleeve them ? Possibly an argument for some sleeving at the lampholder end, but not over the whole length. So logic suggests the cores are in fact only single insulation and the DI is done with the sleeving.
So when the vendor says it's OK, are they lying, or just ignorant of electrics and regurgitating what they've been told ?

 

[ban-all-sheds]

In this case it is the maker who is saying DI.

So if they are not then that is a lie. Unless the maker wants to try a defence of "actually we don't have a clue about what we are making".