Should planning permission be given to build on brownfield land?

"Green belt" land means areas of countryside around some towns and cities, which are currently protected from most building to stop urban sprawl. "Brownfield" land means land that has previously been built upon, such as derilict buildings and former industrial land. "Greenfield" land is land that has not previously been built upon, such as agricultural land outside the greenbelt.Thinking about these different types of land, how freely - if at all - do you think planning permission to build should be given in each one? Brownfield land