Here's an interesting demonstration in the real world of what a difference a decent installation and modern technology makes. Guy in a 6-bed house with bits dating back to the 19th century, was paying £1,970/year to heat with a gas boiler. Got a heat pump 5 years ago that was installed badly and found himself using less energy but as electricity is more expensive he was paying £3,190/year.
Got the system sorted properly with a replacement Vaillant Arotherm+ heat pump and is now paying £1,440/year (ie £530 less than gas) and if he went to the Ovo heat pump tariff it would be £754 (saving £1,216/year, but still looking at a 8+ year payback period if the installation had been from scratch).
They're very happy with how it's now working, he says it's "boring" how every time he looks at it it's a rock steady 20C, and it's more comfortable as it's more radiant rather than convection-based. They used to close off rooms they don't use whereas now they leave all the doors open. From a technical POV, it's notable that since installation they've put 1,112kWh in and got 4,961kWh out for a multiplier (SCOP) of 4.46, and in the last 30 days it's had a SCOP of 5.23.
Towards the end they show
https://heatpumpmonitor.org/ which allows people to display their current SCOP in a league table - it's striking that of the 34 installations with a current COP >=4.5, sixteen are Vaillant Arotherm+,three are Samsung Gen 6 and two are Mitsubishi Ecodan, although the top of the COPs at the moment is a Nibe F2050-10 with a COP of 6.0.