Just been comparing the net present cost (NPC) of my previous domestic combined gas and electricity costs. The last quarter   -  December 2020  to February 2021  Historically  a fairly conventional gas boiler and hot water domestic heating. Electric lighting and sundry domestic power requuirements. 2016 Gas boiler replaced by an air source heat pump. Combined gas and electricity costs. Old system NPC cost  (ie bills would have been at todays prices)  ~ £560 Current