My SEDBUK calculation comes to about half yours and you're using about twice as much gas as me for those periods, so I think it all sounds right. I have a bigger house but better insulated. Loft insulation is very cheap if you do it yourself, pretty cheap if you can get it done subsidised.
The price calculation in your original post sounds wrong though. 400 units would be maybe 150 quid in a month? Maybe a little less on one of the cheapest tariffs.
The price calculation in your original post sounds wrong though. 400 units would be maybe 150 quid in a month? Maybe a little less on one of the cheapest tariffs.