Interesting about interlocked sockets, not some thing I was considering, my worry was more about TN-C-S or PME supplies out doors. In order to stop indoor equipment being used out doors the 16 amp blue socket has be used out doors, or where likely to be used out doors, this means to get power for power tools we have to use the 110 volt transformer and 110 volt tools as we can't simply bring tools from home and plug it. Because metal work in the building is bonded, and this metal work extends 8 miles out doors in the form of railway tracks, it is impossible for the earth to be lost.
But still same rules apply, and in the main out doors we use RCD protection and class II equipment. So the blow up hot tub is OK as class II, until a patio heater class I placed close by. With the pandemic there have been a lot of semi-out door units, it seems we have a nation under canvas. We have had canvas and rubberised building for years, but not so many, cinema where I use to live had a lovely brick built facade but the back was canvas never watched films in the winter.
But we have loads of temporary structures which are supplied for sockets never designed to have class I items used from them. And we have a situation where owners may be unaware sockets being used out side, and installers never intended them to be used out side, and the user is unskilled.
I had even as a professional not considered the way the earth is connected with yellow brick transformers, the line and neutral are isolated, but then the earth is not, so line 1 and 2 may be 55 volt from the PEN voltage but what is the PEN voltage?
Basic question is if TN-C-S is safe?