CPRE seem to have received plenty of coverage for their report highlighting a 'renewed threat' to the Greenbelt.
The report identifies projects "amounting to the development of a new town greater than the size of Slough over the next twenty years".
That's not a unit of measurement I find very intuitive. However, the BBC translates this as about 1,000 hectares. The Greenbelt is currently 1,619,835 hectares. So in a twenty year period the plan is to use a little more than half of one percent of Greenbelt land to help manage growth in UK cities. In terms of undeveloped land that's an even smaller percentage (because Greenbelt itself only accounts for around 12% of England).
It does make you wonder how government (local and national) can be expected to plan sensibly for the development of our towns and cities if using such a small area of land leads to accusations that they are betraying promises on the Greenbelt?