42% of all heat loss in UK homes is via air losses. UK homes are the most air-leaky in the western work as the building regs are not enforced. An air door test should be mandatory on all new and renovated homes.
Leaks are otherwise known as ventilation. You either need a heat exchange unit with blown air, eg fan, or you have leaks. There is the moisture generated by people to deal with. Keep it inside and you will have other problems.
Homes lose 100% of the heat input. Fact.
Zero Heat homes are real and cost nothing more to build than any other house.
This is possible, but not with the required housing density in the uk. The walls would be too thick, and there is still difficulty even if you WERE to use straw bales.
Most of the rest of your post has some merit, but even if we were to "save the planet", what happens to the money people have saved?