The orginal returns are now available for free, by download from the National Archives DocumentsOnline service. Some knowledge of the geographical and administrative boundaries in1851 is helpful to locate these records. There are 623 bundles of records organised by Registration districts within Counties. The process of accessing them is a little convoluted the first time, but stick with it.
Start here http://discovery.nationalarchives.gov.uk/SearchUI/browse/C8993?v=h from which point there are links to 57 county pages. Within each county page will be found the Registration district bundles.
Select one of these bundles which will have number like HO129/xxx. Click “Add to basket”. Then move to the basket (top right of the screen, then “View basket”). Add your email address and “Checkout”. After you submit your order you will receive a download link to the file. The files will be large (100MB) and contain a zip file with one Adobe pdf file. This file is a collection of the images of the actual census return forms. This is where some local knowledge will be helpful in locating the form for a specific place of worship.