Did a quick experiment today. Last night I changed the heating to be always-on, with the thermostats set to either 18 or 20 degrees C depending upon the zone.
The smart meter displays cost of energy since midnight, and I just checked at 2230 when the coat today was £37.66 for gas, that’s £40.17. I think electricity was £6.70.
It’s a comfortable temperature throughout the house now, so it will be interesting to see whether it costs less tomorrow to maintain the temperature.
At £40 per day the experience by won’t last long!