"The Integrated Census Microdata (I-CeM) project was a three-year programme which has produced a standardised, integrated dataset of most of the censuses of Great Britain for the period 1851 to 1911.
By making available to academic researchers the detailed information about everyone resident in this country collected at each decennial census from 1851 to 1911, the I-CeM project has transformed the research landscape for work in the economic, social, and demographic history of this country during a period of profound change in the wake of the industrial revolution."
This statement comes from the main I-CeM introduction at the University of Essex. The project allows users to obtain statistical information from the censuses from England and Wales from 1851-1861 and 1881-1911, and Scotland from 1851-1901 (no, I don't know why England and Wales are missing the 1871 census). The project is outlined at http://www.essex.ac.uk/history/research/icem/default.htm whilst the database itself is accessible at http://icem.data-archive.ac.uk/#step1. There is also a detailed user guide is available at http://www.essex.ac.uk/history/research/ICeM/documents/icem_guide.pdf
British Genes blog.