A (then) nationalised industry - British Gas - managed to convert the whole gas network, which was extensive, but patchy, over to natural gas in the 1960s.
It was under the leadership of a giant of a man, size and intellect - calles Sir Dennis Rooke. He even saw off Mrs Thatcher and kept the gas industry as one when it was privatised, although it was later broken up (after he had gone).
We could have a similar programme for insulating properties. Standards could be drawn up, systems developed for non-standard houses. British Gas converted appliances up to 100 years old - and almost any gas applience ever produced. It should be possible to do this with insulation and older properties, for example.
Obviously the cost could be phenomenal, but for most circumstances the government should pay up front, launch investment bonds with a reasonable interest and recoup the money by putting an interest free charge for the cost the land registry record and the money could be repaid when the house next came on the market - rather like we financed a recent extension with a Retirement Interest only Mortgage - only in this case without the interest.
For commercial and industrial buildings, interest could be charged, but chargeable against tax.
I think house building should be directed. Local Authorities should assess what type of accommodation is needed in an area - how many 1,2,3 etc bedroomed properties. leave decisions about houses/flats to the developers.
I live in an area where 4 bedroomed detached properties are bing built in hundreds, but the price of smaller properties remains high because not enough are being built. I alsonthink we should try to move back to the 1960s/70s when a third of our housing stock was in the public sector and I would see rents in the public sector based on income, not market rates.