Guy, can you tell me why their is only 30 years closure for Overcrowding Surveys but 100 years for Census's 
bendywendy
Yes the answer is very simple M.Ps. were lied to before they voted on the Census (Confidentiality) Act 1991.
The person who lied to them was later made to address the M.Ps. and apologise but by then the Act had been passed and was law.
The first 100 year rule came into being in 1966 by a Lord Chancellor's Instrument (no.12, issued in 1966). This was making use of the option in 1958 Pubic Records Act to vary access to any public record for varying periods of time (mainly because the particular record was in constant use and public access would disrupt this).
It is interesting to note the Registrar General added an unlawful assurance to the 1981 Census that it would be closed for 100 years and he was forced to apologise for his error.
Censuses in the past were commonly released 50 to 80 years after they were taken.
The Freedom of Information Act 2000 has made the current situation that all public records are open to inspection unless there is a reason for that particular record to be withheld.
Each individual record is supposed to be dealt with by itself rather than as part of a class of records. Though in reality each class of records is generally given a closure period of commonly up to 30 years.
All current 100 year rule closures are non-statutory, that means they do not have the authority of law (statute).
Under the Census (Confidentiality) Act 1991 no other census may be released to the public ever.
It will require a change in the law to allow the 1921 census to be released in 2022 as the National Archives claim on their website.
Cheers
Guy
