You're joking of course ( I think ), but you make an important point.
All three UK agencies ( Office for National Statistics / ONS in England and Wales ; General Register Office for Scotland / GROS ; and Northern Ireland Statistics and Research Agency / NISRA ) have agreed to conduct the Census on the same day. They say they are paying " special attention to hard-to-count and under-represented groups" . These include ethnic minorities, disabled / elderly, faith communities, migrants, non-English speakers, unemployed, people on low income, students and other young adults, gypsy, traveller and other groups "whose response has been historically low".
The Government does need information for policies and public services like health and education. The ONS claim the benefits of the Census outweigh the cost of its collection. A review of the last Census (2001) concluded that if a national identity register could be developed it might remove the need for a Census in the future.
There may indeed be "lies, damned lies, and statistics" Certainly the "hard-to-count" groups form a significant number, and unless the information in the Census is accurate it's a waste of time . A carefully taken significant sample of the population, required by law as with the current Census, might be more cost-effective