Compared to most other countries the UK has lots of green and pleasant bits you could build houses on and lots of other bits that are neither green nor pleasant but similarly lacking houses. A great deal of this land without houses on is called "green belt".
In Swindon, for example a big chunk of greenbelt is bog land you can't even walk a dog over. it certainly isn't suitable for growing crops or any kind of farming. However, any plans to build on it are met with massive protests. This position is mirrored country wide.
The Adam Smith institute estimated 1,400,000 families could be housed if the UK lost 1.5% of the greenbelt.
Yesterday's white paper was disappointing because the greenbelt issue was dodged. The one chance for the government to insist that serious amounts of land were made available for new build wasn't taken.
Until we tackle the green belt issue we are never going to have enough houses.