Most of England has last mile connectivity from BT, the historical monopoly telco. BT is required by the regulator to sell access over their "last mile" of copper, fibre, or whatever, at a fixed tariff, plus to sell routing over their long distance networks for a fair price, so that ISPs, even relatively small ones, can serve anybody with those last mile lines, from anywhere in the country. So maybe you pay Jim's Tiny ISP £29 pcm, Jim's pays BT say £8.26 pcm to reach your home, and they've got £20.74 to buy upstream bandwidth, pay staff, taxes etc. The box in your house either belongs to you or was sent out by Jim's, the fibre or copper between your house and some big building belongs to BT, fibre between the building and Jim's Tiny ISP is either owned by BT or a rival huge corporation.
Anyway for a good many years now, BT offered to basically do fibre rather than copper for the same install price on new homes so long as the builders actually had their people come in early and put the trenches where they need to be etc. on a multi-home site during construction. If you wait until the house is finished, BT wants $$$ to dig everything up and lay fibre.
This meant if the house builders understand why owners would want Internet, or if they at least understand market forces, they would pull their finger out and arrange this, because it's basically free money. Some fraction of buyers will actually remember to ask if the new house has decent broadband, and at some point vague non-committal answers either become specific (and actionable if you were lying) or the buyer walks away.
But if the house market is booming, and you don't get into the habit of having BT do their work early in development, you're going to keep building houses which don't have fibre, they'll sell anyway. This government rule tells builders nope, either show why that it'd be crazy expensive to run fibre up a mountain or whatever - or else pay up and get it done, whereupon of course that's pressure on builders to do it properly.
I expect the net price will be almost zero, because of scale.