We mostly report data based on postcode as they are publicly adopted by people and business. They also have a hierarchy - area, district, sector. The hierarchy allows to aggregate data on various data volume and allows to compare different areas, districts, and sectors.
For population we report based on administrative geographical hierarchy which consist - of LSOA (Lowe Layer Super Output Area), MSOA (Middle Layer Super Output Area), local authority district or LAD, county and region level. LSOA and MSOA units were designed to improve the reporting of small area statistics and they were used in Census reports. Also unmeployment, and salary statistics are published on local government level.
Postcode boundaries occasionally change. We use postcode boundaries from 2012.