Firstly, sorry for not getting back to this earlier - one of those weeks!
I have to admit those figures were not clear at all to me so thanks
@AJAM @Zenith63 and
@Leo for looking into all this in such detail and clarifying, very much appreciated.
Just have a few followup questions
1. COP factor, I presume this is the same for everyone but varies according to the temperature outside?
2. Presuming you had a well insulated, airtight house, I take it that a heat pump would be cheaper to run than a gas boiler once you got the initial temperature in the house to an acceptable level?
3. Would you expect that it would take much extra work/much extra disruption if, after adding external insulation and new windows and doors, airtightness turned out to be an issue?
Thanks