Derek Geldard wrote:

There was a previous system some indeterminate time ago in the dark
ages when storage radiators had a hard wired circuit of their own run
through a "White meter".

That's not quite as I recall things. The original 1960s "off-peak"
system provided a time-switched storage heater supply via a separate
meter, but this was not referred to as a white meter.

"White meter tariff" came along toward the end of the 60s and was the
same principle that we now call Economy 7, i.e. a 2-rate meter and an
optional switched supply for storage heaters.

Users could not take advantage of the night rate to run their other
appliances unless they broke into the hard wired circuit.

Which of course they did. That's probably one reason why white meter /
E7 was devised.

OTOH the stotage heaters got a short "boost" during the afternoon.

You can still get, I think, "Economy 10" tariff from some suppliers,
giving something like 00:00 - 05:00, 13:00 - 16:00, and 20:00 - 22:00 at
a cheaper rate (but not as cheap as the E7 night rate).

--
Andy