This was a well known problem identified in the 15th ed. When the 16th ed was released kitchens were removed from the endangered list of special locations and the problems suddenly disappeared. and now with the advent of RCDs, the problems are more or less non-existent - NOT.
I believe the best answer to this was from Approved Document P. The use of supplementary bonding and or RCDs in special locations and Kitchens. Note that Kitchens were a special case all on their own since nobody wanted to call them a special location but couldn't ignore the fact that there might be a probability of extra risk.
I never understood why kitchens were removed from the list of special locations since it was the death of an MPs daughter which spurred the Part P into action.
However, the saving grace of the regs is that all the premptive methods required to reduce the likelihood of shock are still in place even though, as in table 41C that no longer takes a front row seat but still has relevance to those who have used it.
Now where did I put that soap box ?......