Many thanks to all who explained the situation regarding metering of
water in the UK. Rates vs meter usage is obvious now I know.

For those who are interested in water usage bans in Aus, then a bit of
info on how it works here in 2 different areas I know well. Both
areas have level of water restrictions level 1 (lowest ban) to Level 5
highest ban). One area seems to have now gone to a permanent Level 2
and it means:
No sprinkler or other irrigation systems during the week. Only hand
watering and drippers between 7-10am and 7-10pm as per the odds and
evens. ACTEW will also grant a general exemption for limited use of
sprinklers on weekends: even numbered houses on Saturdays and odd
numbered houses on Sundays, and only between 7-10pm, no other times.

The other area has had Level 5 restrictions for at least 2 years and
that means:
Each household is asked to use only 150 litres per person per day (in
the house). No outside use of water whatsoever for any purpose and
fines apply for misuse.