The obsession of London's politicians with their 'green belt' really is a crying shame. But, as this quote from Joel Kotkin tells us, it's not a problem unique to the Home Counties:
To meet the needs of its increasingly diverse population, and particularly the next generation, California needs to reform its regulations to more fully reflect the needs and preferences of its citizens. Once the home of the peculiarly optimistic “California Dream”, our state is in danger of becoming a place good for the wealthy and well-established but offering little to the vast majority of its citizens who wish to live affordably and comfortably in this most blessed of states.
When you have to pay half a million pounds to buy an ex-council flat in Stockwell there is something wrong. Seriously wrong. And anyone who tells you the planning system - the means by which we decide which chunks of land can have houses built upon them - is not the main reason is simply deluded.