Our house is a  Victorian terrace in South London which we retrofitted in 2021-22 to make it as energy efficient as possible (and other improvements).  We have an air source heat pump linked to a conventional heating system with water tanks, radiators and some under-floor heating.  We also have an MVHR ventilation system.  We did a number of things to improve insulation to make this possible and to ensure it is an efficient system.  Our Energy Efficiency Ratio is now 1kwh: 3-4kwh