The govt doesn’t want to get involived in insulating homes because it would be very messy. Firstly it would be hugely disruptive to the economy, where does the manpower come from? Second, simple measures that are diy projects can help a lot, loft insulation for example. Cavity insulation was being supported years ago and if homes don’t have it now why? Social housing has had its own route to supported improvements, You are left with private landlords who have been dragging their feet, they should not need support, and the hard to do houses, like the 1930s houses in their 100,000s without cavities and with suspended floors. There will be old Victorian teraced houses too. The issue there is that the work is very disruptive and best done when the house is empty. Would buyers and sellers tolerate the requirement to do the work during the sales process? That is in a period without occupation, rip up the ground floor to insulate it and deal with the wall insulation. There would be a reality check that a lot of those houses are overpriced! Presumably at some point requiring homes to have a heat loss spec as is to be required for rental properties is the answer.