A while back I turned up a reference to Tolkien's having been the vice-president of the Oxford chapter of the Catenian Association, a fraternal order of Catholic laymen. A little further checking brought to light a mention of Tolkien in an editorial in their newsletter (CATENA No. 868, Feb. 2002, page 3). After mentioning the "unprecedented success" of the first Peter Jackson film, the editor goes on to mention that
"the author JRR Tolkien was of course a Catenian. A Birmingham man, he was Professor of English at Oxford and was Founder Vice President of Oxford Circle in 1944 into which Frank Pakenham (later Lord Longford) was initiated. In 1945 at the second annual Circle dinner, Brother Tolkien proposed the toast to Provincial Council, (according to Peter Lane's account in the history of the Association) 'in a most amusing way which included an actual toast in Anglo-Saxon'."
I've also found another reference which states that Tolkien was that chapter's President from 1945-1946 and remained active through at least the early 1950s; this accords with the brief account in the Scull-Hammond COMPANION & GUIDE (Vol. II p.958) which cites an unpublished letter regarding a group dinner from 1951.
Peter Lane's account is no doubt the book THE CATENIAN ASSOCIATION 1908-1983: A MICROCOSM OF THE DEVELOPMENT OF THE CATHOLIC MIDDLE CLASS ; I've ordered a copy and will post again after it arrives if there's anything more about Tolkien in it.