Thanks, Stefek, this was most helpful.

I went round the house and switched various loads on and off. I
measured the "with load" and "without load" current through the live
incomer using a Fluke clamp meter. I recorded the following readings
(difference between "with" and "without"):

Tumble dryer = 11.9A average, 16.0A peak
Dishwasher = 13.6A for at least 10 mins
Electric cooker (two ovens on full, no rings on) = 18.7A
Electric cooker (four rings on full, no ovens on) = 25.3A
Microwave oven (Cat D) = 7.0A
Electric kettle = 9.2A
Toaster (two slice) = 3.1A
Hair Dryer = 7.3A
All lights on (40 bulbs) = 11.6A
Electric fan heater on full = 11.6A
Washing machine = [still to test]

The point of my original post was not how expensive or inefficient it
would be to use all the above at the same time. It is that, worst
case, you could conceivably consume near the 100A single phase limit
with standard appliances.