It's not adding much actual cost, but you know they will use it to claim that it is so they can pass it on.
Homebuilders may argue that it’ll increase costs that’ll need to be passed on when they’re lobbying against these sorts of measures but once passed, it’s done. It wouldn’t enter into the discussion with a buyer.
“Hey, we’d have sold you this property for £300k but since the government forced us to give you faster internet we’ve had to bump the price a couple of grand”