A very interesting thread; thank you to all contributors.  My own experience is that present-day accessories may be the weak link here. As mentioned above, present-day accessories seem to be manufactured to the lowest feasible BOM, overseen by anxious bean-counters. As a legacy situation, on moving into Chez Jenkins in 1996 I encountered a utility room with a surface-mounted plastic twin 13 amp socket, manufactured by Tenby, under a worktop. The utility room is the only practicable place for the washing machine and the tumble dryer, so that is where they went, both plugged into the same socket, which had been there since the utility room was added in 1980.  I did not mention any usage restrictions to the Senior Management, and elected to let things run just as they are, but to keep a very close eye on the welfare of the twin socket. It never even got warm - ever, and I soon lost interest in fretting about its welfare.  A gradual rewire of the cottage ensued over the years, during which I noticed the change in quality of electrical accessories. This to the extend that I carefully cleaned and checked all the existing accessories from 1980 and re-installed nearly all of them rather than replace them with new ones, only installing new accessories for additional facilities. The utility room came up for a major refit in 2020; time to deal with that Tenby twin socket. On removal, it looked like it had just left the factory! Thus, it's back under the worktop, in the same Tenby surface plastic box, running the washing machine and tumble drier with no restrictions and looks like it will do so for another 40 years with no bothers. I have regularly checked it since the re-fit, and, just as before, it doesn't even get warm. Sadly, I would not be so relaxed about any of the modern accessories and would follow Graham's guidance if faced with this elsewhere.

A very interesting thread; thank you to all contributors.  My own experience is that present-day accessories may be the weak link here. As mentioned above, present-day accessories seem to be manufactured to the lowest feasible BOM, overseen by anxious bean-counters. As a legacy situation, on moving into Chez Jenkins in 1996 I encountered a utility room with a surface-mounted plastic twin 13 amp socket, manufactured by Tenby, under a worktop. The utility room is the only practicable place for the washing machine and the tumble dryer, so that is where they went, both plugged into the same socket, which had been there since the utility room was added in 1980.  I did not mention any usage restrictions to the Senior Management, and elected to let things run just as they are, but to keep a very close eye on the welfare of the twin socket. It never even got warm - ever, and I soon lost interest in fretting about its welfare.  A gradual rewire of the cottage ensued over the years, during which I noticed the change in quality of electrical accessories. This to the extend that I carefully cleaned and checked all the existing accessories from 1980 and re-installed nearly all of them rather than replace them with new ones, only installing new accessories for additional facilities. The utility room came up for a major refit in 2020; time to deal with that Tenby twin socket. On removal, it looked like it had just left the factory! Thus, it's back under the worktop, in the same Tenby surface plastic box, running the washing machine and tumble drier with no restrictions and looks like it will do so for another 40 years with no bothers. I have regularly checked it since the re-fit, and, just as before, it doesn't even get warm. Sadly, I would not be so relaxed about any of the modern accessories and would follow Graham's guidance if faced with this elsewhere.