Here’s an idea, if you drive on any road going out of any village, town or city into the country you inevitably come to the last house on that road.
I would suggest you could build a house on a plot next to the last house even if it was on green belt land and because it is roadside its impact would be minimal and not encroach on valuable farmland. I have to wonder how many houses could be built under this system? Hundreds of thousands, millions maybe, I would say.
There should of course be the usual safeguards of planning and maybe a rule that forbids building on a next plot for 10 years.