The announcement drew little attention next to her inheritance tax bombshell, but it would reach more people. The UK needs roughly 6m new homes, and skipping efficient, low-carbon energy sources would saddle households with higher bills for decades.
The Tories quoted estimates of 30,000 per new-build house, but the real cost is likely much less. Heat pumps, solar panels, batteries and insulation cost about 5,000 to 8,000 to install during construction, based on a 2024 estimate, and save more than 1,300 a year on bills.
Jan Rosenow, a professor of climate and energy policy at the University of Oxford, said every home built today that runs on fossil fuels is a liability for the people living in it. He wants less political point scoring and more long-term clarity.
The UK Green Building Council says the construction industry is well prepared and will have to implement the policy before the next general election, so scrapping it brings little benefit. Housebuilders have been among the Conservatives' biggest donors, though that has fallen off in recent years.
Elsewhere, the Greens backed new nuclear reactors and Labour put oil-drilling decisions on hold.
Bolting it all on later would cost more than 20,000.