Thank you all for your replies.The narrative report goes some way to giving me what I am looking for by directing me to my hard copy of the source (I use a numbering system such as CEN01/xxx for a 1901 census sheet). It would be an advantage to be able to select the source detail ref # in a custom report.
Thanks for the replies - I was coming to the conclusion that that might be the case, which is a shame. It does seem odd that the input field is available but the field is not available in the custom report - seems a little pointless to have it in the first place. Perhaps RM needs to look at this.
Thanks again I'll have look at the SQL as suggested.