Overall, it's using a truckload of gas... probably close to the £200pm you mention.
Just that the boiler heats up the CH water to 72 deg and then stays there. It doesn't use much to keep it at 72 deg (the meter rotates quite slowly - say 1 cu. ft/min). When the boiler is warming up the water from start it guzzles the stuff!
Probably using between 4-8 imperial units a day at the moment. It's on less in the weekdays since the house is empty for a lot of the day.
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