Running cost comparison
Gas is usually cheaper per unit than electricity, so a heat pump needs good seasonal efficiency to compete on bills.
The stronger the SCOP and the lower the boiler efficiency, the more attractive the heat pump becomes.
Comfort and system design
Heat pumps tend to perform best with longer, steadier heating cycles rather than short bursts of high heat.
Radiator sizing, hot water setup, and weather compensation can have as much impact as the equipment brand.