Housing benefit/Council Tax benefit, which is council housing's evil twin (housing benefit is current spending that effectively supports high rents, where what is needed is long-term investment in social assets to reduce rents), looks set to cost us
an eye-watering £30bn pa. It has almost tripled since 2000. There is no shortage of money just governmental short-sightedness.
The government could borrow at low rates to build, or it/councils could issue bonds to savers, or it could use QE/Overt Monetary Financing. The long-term deflationary effects of having housing stock built to near-passivhaus standards are obvious: no need to import as much gas/oil; no need for as many new power plants; the money put into the economy would create housing stock whose rents would not need to rise at the same rate as property prices, etc. Start now - create designs for eco-housing that can be built with predominately British materials (a series of supply chains that may need to be built), and train a British labour pool to tackle the job - and then build at a sustainable rate over the next twenty years or more.
Anything we can actually do, we can afford, as Keynes said.