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Access 1991 Census aggregate data through Casweb
The aggregate data produced as outputs from censuses in the United Kingdom provide information on a wide range of demographic and socio-economic characteristics. They are predominantly a collection of aggregated, or summary counts of the numbers of people, families or households resident in specific geographical areas possessing particular characteristics drawn from the themes of population, people and places, families, ethnicity, work, and housing.
Office of Population Censuses and Surveys ; General Register Office for Scotland ; Registrar General for Northern Ireland (1997): 1991 Census aggregate data. UK Data Service (Edition: 1997). DOI: http://dx.doi.org/10.5257/census/aggregate-1991-1
You will be able to access 1991 Census aggregate data at UK Data Service.