You asked
I am requesting data on the budget enacted for the ONS each year from the 1950s-2016 and the number of staff (FTE) each year.
We said
The ONS was formed on 1 April 1996 by the merger of the Central Statistical Office (CSO) and the Office of Population Censuses and Surveys (OPCS). Following the Statistics and Registration Service Act 2007, the United Kingdom Statistics Authority became a non-ministerial department on 1 April 2008.
The attached link to the Annual Report and Accounts contains the relevant information for the current organisation.
https://www.statisticsauthority.gov.uk/publications-list/?type=annual-report-accounts