One solution, would be for Ofcom to allow the use of the Internet, as an acceptable option to relay consumption figures, to suppliers. Octopus already do this, using their pink thingummy. I have one, and it works a treat, feeding a constant stream of my instantaneous figures, every 10 seconds, to Octopus, but it is unofficial, I cannot be billed using it.
I had one from Scottish Power, must be some 20 years ago now, and the bills were based on what it said, and corrected when an actually reading was made, and always within £10 of what we had been billed over the year, still have the device, it has a CT coil and a battery transmitter, very like the one used with the iboost+ and a display very like the IHD which also plugged into the router, and seem to remember 3 socket energy monitors also came with it. (they stopped working)
And for a single rate tariff, the system worked well. Really no point in a smart meter.
But for a dual rate tariff, they were not good enough, I could unplug it from the internet, and clearly if my internet went down it stopped working, and clearly the time needs to be reasonably accurate. With the British Gas EV tariff I was on, the smart meter and the IHD did not agree on time. Winter it was OK, but Summer one showed daylight saving time, and the other showed unified time constant (UTC). It was claimed to get off-peak midnight until 5 am, so set it 1 am to 5 am to be sure.
With my battery charging, it took 90 minutes, so it did not really matter where in the 5 hours I did the charging. As to how fast storage radiators heat up, not sure, I would assume less than 7 hours, but how accurate it needs to be I don't know? If it takes 6 hours to fully charge, then could start charging ½ hour after change over, and stop ½ hour before change over, so as long as clock within ½ hour between meter readings no real problem.
But I would think there would need to be some British Standard as to how much the measurements can be out, either in kWh or time, and the new "suitable meter" will need to comply to these standards. A quartz clock which is corrected from the internet, or radio can keep good time, my car seems to use something, as the radio clock seems to change the hour when added or removed reasonably quickly, I assume radio data service (RDS) corrects it.
We have the technology, what the teleswitch did, which a RDS or internet can't do, is to vary the start time so we don't get every off-peak device turning on together. With "smart" meters, that has already been lost. I don't get a signal from the meter to tell me when to start charging, it is up to me to set the device, which may or may not be at 11:30pm/midnight/or 2am depending on the tariff used.
But we are now into the 11th hour, so by now we should know how it is going to be done.