Quote from the North Wiltshire Retail needs assesment study:

In assessing expenditure growth, we have applied the ONS 2004 based population
forecasts 5 for North Wiltshire, West Wiltshire and Kennet, having allocated each of our
nine household survey zones to the district in which all or the majority of the population
in that zone falls (see Spreadsheet Table 1). Thus, the population change in each
zone is as set out in Spreadsheet Table 2. For the catchment area as a whole, the
population is projected to grow from 183,335 in 2007, to 203,821 in 2026, a growth of
11.2%. The fastest growing zone is Melksham which is located in West Wiltshire
District.

I confess to my initial post being deliberately worded to be a bit of a 'teaser' 

Here are the links to the full reports:

Website:  http://www.northwilts.gov.uk/index/env/planning/localplans/ldf_studies_.htm

PDF report (2.9mb) :   http://www.northwilts.gov.uk/retail_needs_assessment_study_2007_full_doc.pdf