There have been major advances in technology since the 1991 Census, particularly in the field of data capture. Census forms were fed through scanning machinery which captured tick box and written answers in digital format, before coding software coded responses to a set of pre-defined classifications. The paper forms were then pulped and recycled with the digital data transferred to microfilm (census legislation allows that this data be made available as public records after 100 years) This part of the Census was contracted out by ONS to Lockheed Martin
The automation of this process has dramatically reduced the clerical work required. A major consequence of this is that it has enabled all questions in the census to be 100% coded. In 1991, a reliance on manual coding meant for many "hard to code" questions, coding was only carried out for a 10% sample.