One of the big problems in the UK is that housing is not built like that. In most of the UK it rarely gets below freezing, yet even new homes come with big gas

One of the big problems in the UK is that housing is not built like that. In most of the UK it rarely gets below freezing, yet even new homes come with big gas boilers because of how poorly insulated they are, and if you turn it off for half a day, it will get cold inside. The housing energy certification in the UK is very misleading, as a home built with walls with a U value of 0.25W/m2K is rated as "very good" (the maximum). Where as in my country all new homes built in the past 5 years have required a U value of less than half that - of course that doesn't tell the full picture as need to know how thick the wall is, but you don't see new UK homes with 1m thick walls. Even with the pretty lax requirements, very few new homes in the UK have an A energy rating. One major issue is that homes are still built the same way as they were 50 years ago with a cavity wall. Facing bricks are porous, so you need to allow water to escape, and the cavity wall is usually open at the bottom and the top (usually into the attic) to allow that. If you were to wrap the interior wall with a layer of 200mm PIR board and ensure it is air sealed, you could have a pretty well insulated wall, but often the cavity is filled with mineral wool pressed tightly against both walls. Then it inevitably gets moist which impacts the material's thermal performance. And that's just one the most basic things, other modern high performance items such as triple glazing, mechanical ventilation and heat pumps are also rare. https://en.wikipedia.org/wiki/Cavity_wall https://en.wikipedia.org/wiki/Cavity_wall