Around 25 million household census questionnaires, plus millions more from care homes, hotels, military bases and other communal establishments, were processed at a secure facility in Manchester.

Questionnaire processing involved data capture, scanning, envelope slitting, sorting, removing spines from questionnaires and shredding all under one roof, subject to rigid and comprehensive security controls.

Questionnaire delivery

Royal Mail made around 280 deliveries to the site during March and April 2011, with each 44 tonne van carrying around 54,000 questionnaires. After they had been receipted, they were stored in a secure warehouse until needed for processing.

Envelope opening

Around 20 envelopes at a time were loaded onto a machine opening 50 envelopes a minute, slitting each along the long side so that it could be easily removed by hand. All kinds of documents turned up with the questionnaires, including marriage certificates and passport applications. Staff passed any such official documents to the relevant authorities and safely destroyed any other unnecessary items found in the envelopes.

Preparing for scanning

Questionnaires were then loaded into a machine to remove the spine and staples that held it together. This machine cut through 30 questionnaires in one go and 650,000 questionnaires a week. Questionnaires were then left for at least 24 hours to acclimatise so that they were in the most suitable condition for scanning.

Data capture

A full set of images from each questionnaire was securely scanned and archived ready for release 100 years later. An image of both sides of the paper was taken simultaneously and fed into the computer. It took just a minute to scan around 15 questionnaires onto a database for processing – and once scanned, they were securely destroyed and recycled.