The 1971 Census was undertaken on the night of 25/26 April 1971. The Census was carried out by the Office of Population Censuses and Surveys (OPCS) in England & Wales and the General Register Office for Scotland (GROS).
The Census questionnaires and table layouts can be downloaded as PDF files below:
1971 Census Private Residents Census questionnaire (PDF)
1971 Census Communal Establishment Census questionnaire (PDF)
1971 Census Small Area Statistics Census table layouts (PDF)
SASPAC System files of the 1971 data can be downloaded from here.
1971 Census definitons and concepts (PDF) for Great Britain.