They are rated class two and should come with double square symbol on, that is the British standard the symbol.
I always thought that meant doubly insulated. OK I can see an argument for the sleeving forming an insulator but it is not very substantial? at least not on the ones I saw. I felt (and may be wrong) that if the sleeving gets old /over heated then it would fragment and then possibly put the line conductor in contact with the metal housing which does not have a CPC.