The modern-day planning system is a post-war invention, traced to the passing of the 1947 Town and Country Planning Act, which established a comprehensive and universal system of land-use control. Then, as now, the system served the key function of balancing public and private interests. Today, the key policy objective is one of ‘sustainable’ development in an attempt to both mitigate and adapt to climate change, so that government planning policy seeks (by 2008) that 60 per cent of new housing is constructed on brownfield land (previously developed land), that housing density exceeds 30 dwellings per hectare (unless an exceptional case) and that development plans promote low carbon development with renewable sources accounting for 10 per cent of energy supply. Land-use change statistics have consistently reported, since the early 2000s, an increase, year on year, in the percentage of development on brownfield land and the density of new development. By 2007, and with the issuing of new national planning policy on climate change (in the ‘planning and climate change’ supplement to PPS1 – ‘Planning Policy Statement 1’), attention has turned to achieving zero carbon development.