You asked
I need information about trends in religious belief between 1880 - 1950, ideally with regard to belief in the afterlife.
We said
Thank you for your correspondence requesting data pertaining to religious belief between 1880 and 1950.
The Office for National Statistics (ONS) does not have the information you are searching for. There were no questions on the topic of religion in any census between 1880 and 1950. A question on religion ("What is your religion?") was included in both the 2001 and 2011 censuses, however this question was used to collect information on religious affiliation rather than philosophical belief. The most recent results from the 2011 Census are available from the Nomis website:
http://www.nomisweb.co.uk/census/2011
There was a voluntary enquiry on religion in the 1851 Census. This open university paper describes it (and two unofficial censuses conducted by newspapers at later dates) in detail: https://www.open.ac.uk/Arts/building-on-history-project/resource-guide/source-guides/religious-censuses.htm
If you have not already done so, you might be interested in looking at the British Religion in Numbers (BRIN) website, an online religious data resource which has a large range of statistics on faith in Britain: http://www.brin.ac.uk/
In particular http://www.brin.ac.uk/figures/#ChangingBelief (7.1 Belief in the Afterlife,1939-2008) shows a table of belief in the afterlife based on polls (YouGov, MORI, Gallup etc) 1939 - 2008.
Please note that the ONS is not responsible for the content of, or veracity of data on, any third-party website.
(BRIN is hosted by Cathie Marsh Institute for Social Research at Manchester University and has at times been sponsored by two publicly-funded UK Research Councils: the Arts and Humanities Research Council and the Economic and Social Research Council.)
If you have any further questions may I suggest that, rather than using the Freedom of Information route, you contact Census Customer Services directly. They will be glad to deal with any census related queries and the process is much speedier.
Web: https://www.ons.gov.uk/census/censuscustomerservices
Email: census.customerservices@ons.gov.uk
Tel: +44 (0)1329 444972 Census Customer Services: ONS, Titchfield, Fareham, Hants, PO15 5RR