To ask the Deputy Prime Minister what mechanism exists to reclassify brown-field sites as green-field sites where the characteristics of a brown-field site are no longer present; and how much land has been thus reclassified since July 2001. 
There are various definitions of a brown-field site. The National Land Use Database (NLUD) uses the definition of 'previously-developed land' (PDL) provided by planning policy guidance for housing (PPG3). The definition excludes land that was
In updating NLUD-PDL records, local authorities should report changes to the status of a site (normally through redevelopment) but information of the type sought is not held centrally and could be provided only at disproportionate cost."previously-developed but where the remains of any structure or activity have blended into the landscape in the process of time (to the extent that it can reasonably be considered as part of the natural surroundings), and where there is a clear reason that could outweigh the re-use of the site—such as its contribution to nature conservation—or it has subsequently been put to an amenity use and cannot be regarded as requiring redevelopment."