I suspect that builders will leave the new homes with no heat if the government makes it difficult. The new owners will have to do the job.
That may be the case but if they want to sell them they would have to have the home with heating.
A comparison of average costs for just the boiler installation in an average house:
Gas Combi Boiler - £1,500
Electric Combi Boiler - £4,000
Ground Source Heat Pump - £10,000 to £18,000
Air Source Heat Pump - £8,000 to £15,000
Hydrogen Combi Boiler - £1,500
The running costs of gas or hydrogen boilers make them the most economical for consumers with electric the most expensive. Ground or air source can be the most economical over a period of time as can be solar but there has to be an additional element of maintenance costs added.