The date of the 1931 census of England, Wales and Scotland was the night of Sunday 26 April 1931. The entire census including schedules, enumeration books and plans were destroyed in a fire at the Office of Works store at Hayes, Middlesex on Saturday 19 December 1942. The fire was not due to enemy bombing in the second world war but was due to an unexplained incident.
There is an interesting letter published on the National Archives website from a W A Derrick of the General Register Office to F C Stobart of the Central National Registration Office. He is mystified as to the cause and extent of the fire, particularly as there were 6 paid ‘watchers’ from the fire service on hand. He states: ‘The fire was not occasioned by enemy action and how it achieved such dimensions in a store in which special hydrants had been fitted and said to have been in charge of a fire guard of 6 paid watchers, is a mystery which will need investigation’. The subsequent investigation the following year mentions a police report and a suggestion that the fire may have actually been started by a lighted cigarette thrown down by one of the fire watchers. No action was taken. Here is the link to letter published by the National Archives.