Something I've been pondering (which falls into the Crazy Idea But It Might Just Work department)...
Much of the cost of heat pumps systems is getting the heat into the building. Conventional rads require high temperatures which HPs can't provide efficiently. UFH is lovely but expensive. Replacing conventional rads with fan-assisted ones is also pretty expensive.
I also note the fashion for stripped floorboards in houses with conventional suspended floors with ventilated under-floor spaces. Presto! under-floor cooling in winter!
So how about an air-to-air heat pump pushing warm air into the under- floor void, with the air-bricks sealed up? The warm dry air should discourage damp problems (the reason for the air bricks and thus the cold air under the floor). Assuming non-tongue-and-grooved floorboards you've got a ready distribution of warmed air through the floor into the ground floor rooms. You may have to duct some warm air upstairs and into solid- floored back extension kitchens and (more importantly) bathrooms in houses with that layout, and you'd need a source of water heating (electric or solar). But as a cheap renewable-friendly system, what am I missing? (Except anyone actually having tried it, natch!)