The second is development control information, following through from planning applications to approvals, starts and completions of developments. The third is the Council Tax register, established in April 1993. In addition, a plethora of other data sources are used. There are valid reasons for the three main data sources not to agree about the status of a particular property at a point in time and also about the overall change to the dwelling stock. Secondly, changes are recorded at different times.
All main sources tend to be underestimates of the real level of activity for a variety of reasons.
The best information about the overall change to dwelling stock probably comes from the Council Tax register. It is not clear how best the various sources can be combined to produce a definitive figure for the overall change to the permanent dwelling stock for planning purposes. While it is not possible to know how much data is missing, it was a common concern at local, county and national level that data are incomplete. Many planners felt that building control completions were either significantly delayed or not issued at all. Since these were relied on for information about new build, this would cause underestimation of additions to the dwelling stock.