The idea to moving everything to heat pumps right now isn't so that you immediately reduce carbon emissions, but that everything works off of electricity and the grid so that as offshore wind, onshore wind, solar and Hinkley Point C come online it can start to replace fossil fuel energy. Same with EVs.
If you stick with gas boilers there is really no exit strategy for getting off fossil fuels.
If you stick with gas boilers there is really no exit strategy for getting off fossil fuels.