endymion wrote:

Having switched them off, whatever the figures ( and 5000+ units in
three months speaks for itself surely as opposed to a total of just 800
for three months on day rate?) they have shown a significant drop in
the night rate usage to less than 10 units a night even when running
the washing machine and dishwasher and even an hour on the tumble dryer.

[...]

However you want to argue the figures , it doesn't alter the fact that
it was the night rate that was up very high ( 5000+ units a quarter)
and that has been changed by switching one heater off ( the only one
that was actually on at the time) It may not seem reasonable but that
is what has happened.

Something just isn't adding up here, even though the night rate
consumption seems to have dropped from an extrapolated 18,000+ units per
quarter to a much more reasonable figure of 5,000(?). 5,000 units over
90 days is 55 per day and with "the heater" switched off this drops to
10. The 45 kWh/day saved implies 6.4 kW load if running for the full 7
hours each day. That perhaps suggests that you've switched off two 3.4
kW size heaters, not one. I'm wondering if you've got two heaters
wired, rather unconventionally, on one final circuit. Certainly your
mention of plugs rings alarm bells as storage heaters should be
permanently wired on dedicated individual circuits (except perhaps for
the smallest size where two per circuit might be OK). The 24 kWh (3.4
kW) size appliance draws over 13 A, so 13 A wiring accessories shouldn't
be used at all, just a 20 A DP switch with flex outlet and a 16 A fuse
or MCB in the consumer unit.

Day rate is 16p a unit

That sounds a bit over the odds.

--
Andy