I have not researched this but someone I know at one of the big house-builders pegged the cost of building a 3 bed at around £35-40,000, so in the south east land with PP is 10X more valuable than what's sat on it.

"Farm" land, even in the SE is about 12K an acre, and you get 6-8 houses to the acre so you should be able build a three bed and sell it for £50K on the outskirts of London, Cambridge, Oxford or Brighton (just by example) still making a profit if we liberalised planning in those areas. That shows you how extreme this situation of fake constraint is.

It could therefore never be allowed to happen. The big house-builders wouldn't build and sell at that price, the locals wouldn't allow it as they've bought their houses for 500K, 10X as much and would literally all go personally bankrupt...