Greenbelt legislation and regulation have some impact on house prices but the argument that it is the fundamental reason can be utterly dismissed by envisioning the scenario where no land-use legislation exists but the city-region population continues to grow and sprawl out from the core.  The greater the sprawl the higher land-prices will be closer to the center regardless of how much land is made available for development at the periphery.

On the other hand envision another scenario where interest rates normalized to 5% driving up mortgage rates to the point where a typical 1 million dollar property would require $5400 per month to carry the mortgage.

Contrast these two scenarios and think about who is promoting the greenbelt=high house prices argument and who wants to hide the real interest rate sensitivity of the housing market.