Speaking of heat pumps, in the last year 30,000 heat pumps were installed, at that run rate it will take 766 years to retrofit 23 million gas boilers without factoring in the units installed in the 15-20 years previously that will be coming to end of life.
Around where I live it is almost all oil fired boilers - when we moved here they'd just stopped some kind of subsidised scheme to replace them with heat pumps, I'm not really sure the details. Those who had air source ones installed as part of the scheme are really not happy with them - especially some have had large electricity bills, the ground source ones seem a bit better received. We really seem to make a muddled mess of this whole thing.