It is not recommended that a homeowner attempts to improve the energy efficiency of their home by simply adding new technologies (for example heat pumps, photovoltaic panels) on their own.
The key to the successful use of these technologies is that the house is insulated correctly and made as draft free and air-tight as possible.
Insulation and air-tightness are indicated by a measurement called Heat Loss Indicator (HLI). For heat pumps to work effectively the HLI must be at a level of less than or equal to 2 W/K. This means that in most cases walls and roofs are fully insulated and older windows and doors replaced.
You can see an energy audit and recommended actions report explained with comments below. It is essential that the homeowner has an audit carried out on their individual home before they decide which measures to take.