I wonder how exactly it costs this much? What is the money spent on?
Lets imagine the 'MVP' census. A printed 10 page document (£0.45), mailed to each household (£0.61), in an envelope (£0.02), times 27.6 million houses. Return mailing costs another £0.61+0.02. Scan every sheet. OCR it (free). Hand-enter 1% of responses where OCR errors are excessive. 276,000 documents hand entered at 5 minutes per document, £10/hr. £0.0083/household. Total costs: £47M
Cost of running a few trial runs of one 10,000 house town or city to perfect the process: £100k
Pay for a year 1 statistician to make graphs, one social scientist to design questions, one manager for the team of printing/scanning/hand-entering people, one IT person to keep/archive the data and get it on the web, and a head of department. Also a little office. Total fixed costs £800k.
The whole thing can seemingly be done for 5% of the quoted cost. And that excludes any potential efficiencies gained by having an app to collect responses, or bulk discounts from postage companies. Also, while a redacted version of the full dataset is published, I would expect the government department to also offer commercial statistics services on the non-redacted dataset where such analysis doesn't impact customer privacy. That should earn them tens of millions at least.