davezawadi (David Stone): 
 

I see your points Graham, but I think you are being misguided as to the possible levels of risk. Whilst Appendix 15 does suggest a degree of care is required it is NOT a regulation and is not usually up to the electrician anyway. From your comments, I would infer that you think that double sockets should not be permitted, or possibly they should only be fed via a 13A FCU. You also imply the 2.5mm cable size is inadequate, whereas I suggest that it is not, and is proven by 10s of millions of installations that it is perfectly satisfactory.

I think you've missed my key point by some way.

Over time, I believe I am coming to the conclusion that the ring final circuit and the fused plug or fused connection unit it requires presents an outdated solution, which wastes energy and resources. I think the most appropriate solution is a 16 A or 20 A radial, with an appropriate unfused plug and [shuttered] socket-outlet, or an unfused connection unit.

To implement this, we needn't require existing installations change - fused adaptors can be used for new appliances, and fused versions of the new socket-outlet design could also be provided for use on ring final circuits.

I suggest that a single socket and a two-way adaptor is much worse than a double socket, but that would be the result of removing double sockets!

I agree.

gkenyon: 
Sorry … the limitations of the ring final circuit are very clear.

If it's not recommended to place a 2 kW oven on the ring final, then it's certainly not recommended to put two heavy current-using appliances on an individual double socket-outlet … this is specifically covered in Appendix 15 of BS 7671 item (iii) … so, what are you actually saying?

The imbalance in my circuit could hardly be greater: the socket is about 1 m from the CU with a far point about 18 m away; but having a CU in a utility room with a washer and drier can hardly be unusual.

The saving grace is App 15: The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable … (my emphasis). Of course a long period is not defined, but an hour or so appears to be fine. 

The ring final highlights just how much slack there is in the book ratings, and how far from reality typical diversity assumptions can be. Because in practice it works very well, despite a  body of theoretical cases when it should not. 

At the risk of sounding like a stuck record, if you compare the wiring practices with less well regulated 230V countries (Brazil, India, China perhaps parts of the former eastern bloc ) where 2.5mm or even 1.5mm singles are used on  breakers certainly up to 32A with nary a problem, in the UK we are incredibly cautious. Of course I take the point that if the wiring is all on the surface and joined with hedgehog splices, then for chunks to be changed when it fails and goes bang  is less of a hassle.

If we really wanted to change our plugs and sockets, then something that takes the Europlug would be good, and we could then remove reverse polarity from out list of faults. And something more waterproof for bathrooms and outdoors. 

(of course the lower current inwardly sprung pins europlug does fit the 13A socket but it is not really intended to )

Mike

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.

Edit: I forgot to say: the present washing machine is 2300 Watts (9.60 amps) and the tumble drier is 2450 watts (10.20 amps). So, both are slightly above Graham's 2kW threshold.